Novel semiconductor and optoelectronic devices

ABSTRACT

A method for fabricating a light-emitting integrated device, comprises overlying three layers, wherein each of the three layers emits light at a different wavelength, and wherein the overlying comprises one of: performing an atomic species implantation, performing a laser lift-off, performing an etch-back, or chemical-mechanical polishing (CMP).

BACKGROUND OF THE INVENTION

(A) Field of the Invention

This invention describes applications of monolithic 3D integration tovarious disciplines, including but not limited to, for example,light-emitting diodes, displays, image-sensors and solar cells.

(B) Discussion of Background Art

Semiconductor and optoelectronic devices often require thinmonocrystalline (or single-crystal) films deposited on a certain wafer.To enable this deposition, many techniques, generally referred to aslayer transfer technologies, have been developed. These include:

-   -   Ion-cut, variations of which are referred to as smart-cut,        nano-cleave and smart-cleave: Further information on ion-cut        technology is given in “Frontiers of silicon-on-insulator,” J.        Appl. Phys. 93, 4955-4978 (2003) by G. K. Celler and S.        Cristolovean (“Celler”) and also in “Mechanically induced Si        layer transfer in hydrogen-implanted Si wafers,” Appl. Phys.        Lett., vol. 76, pp. 2370-2372, 2000 by K. Henttinen, I. Suni,        and S. S. Lau (“Hentinnen”).    -   Porous silicon approaches such as ELTRAN: These are described in        “Eltran, Novel SOI Wafer Technology”, JSAP International, Number        4, July 2001 by T. Yonehara and K. Sakaguchi (“Yonehara”).    -   Lift-off with a temporary substrate, also referred to as        epitaxial lift-off: This is described in “Epitaxial lift-off and        its applications”, 1993 Semicond. Sci. Technol. 8 1124 by P.        Demeester, et al (“Demeester”).    -   Bonding a substrate with single crystal layers followed by        Polishing, Time-controlled etch-back or Etch-stop layer        controlled etch-back to thin the bonded substrate: These are        described in U.S. Pat. No. 6,806,171 by A. Ulyashin and A.        Usenko (“Ulyashin”) and “Enabling SOI-Based Assembly Technology        for Three-Dimensional (3D) Integrated Circuits (ICs),” IEDM        Tech. Digest, p. 363 (2005) by A. W. Topol, D. C. La Tulipe, L.        Shi, S. M. Alam, D. J. Frank, S. E. Steen, J. Vichiconti, D.        Posillico, M. Cobb, S. Medd, J. Patel, S. Goma, D.        DiMilia, M. T. Robson, E. Duch, M. Farinelli, C. Wang, R. A.        Conti, D. M. Canaperi, L. Deligianni, A. Kumar, K. T.        Kwietniak, C. D'Emic, J. Ott, A. M. Young, K. W. Guarini, and M.        Ieong (“Topol”).    -   Bonding a wafer with a Gallium Nitride film epitaxially grown on        a sapphire substrate followed by laser lift-off for removing the        transparent sapphire substrate: This method may be suitable for        deposition of Gallium Nitride thin films, and is described in        U.S. Pat. No. 6,071,795 by Nathan W. Cheung, Timothy D. Sands        and William S. Wong (“Cheung”).    -   Rubber stamp layer transfer: This is described in “Solar cells        sliced and diced”, 19 May 2010, Nature News.        With novel applications of these methods and recognition of        their individual strengths and weaknesses, one can significantly        enhance today's light-emitting diode (LED), display,        image-sensor and solar cell technologies.

Background on LEDs

Light emitting diodes (LEDs) are used in many applications, includingautomotive lighting, incandescent bulb replacements, and as backlightsfor displays. Red LEDs are typically made on Gallium Arsenide (GaAs)substrates, and include quantum wells constructed of various materialssuch as AlInGaP and GaInP. Blue and green LEDs are typically made onSapphire or Silicon Carbide (SiC) or bulk Gallium Nitride (GaN)substrates, and include quantum wells constructed of various materialssuch as GaN and InGaN.

A white LED for lighting and display applications can be constructed byeither using a blue LED coated with phosphor (called phosphor-coated LEDor pcLED) or by combining light from red, blue, and green LEDs (calledRGB LED). RGB LEDs are typically constructed by placing red, blue, andgreen LEDs side-by-side. While RGB LEDs are more energy-efficient thanpcLEDs, they are less efficient in mixing red, blue and green colors toform white light. They also are much more costly than pcLEDs. To tackleissues with RGB LEDs, several proposals have been made.

One RGB LED proposal from Hong Kong University is described in “Designof vertically stacked polychromatic light emitting diodes”, OpticsExpress, June 2009 by K. Hui, X. Wang, et al (“Hui”). It involvesstacking red, blue, and green LEDs on top of each other afterindividually packaging each of these LEDs. While this solves lightmixing problems, this RGB-LED is still much more costly than a pcLEDsolution since three LEDs for red, blue, and green color need to bepackaged. A pcLED, on the other hand, requires just one LED to bepackaged and coated with phosphor.

Another RGB LED proposal from Nichia Corporation is described in“Phosphor Free High-Luminous-Efficiency White Light-Emitting DiodesComposed of InGaN Multi-Quantum Well”, Japanese Journal of AppliedPhysics, 2002 by M. Yamada, Y. Narukawa, et al. (“Yamada”). It involvesconstructing and stacking red, blue and green LEDs of GaN-basedmaterials on a sapphire or SiC substrate. However, red LEDs are notefficient when constructed with GaN-based material systems, and thathampers usefulness of this implementation. It is not possible to depositdefect-free AlInGaP/InGaP for red LEDs on the same substrate as GaNbased blue and green LEDs, due to a mismatch in thermal expansionco-efficient between the various material systems.

Yet another RGB-LED proposal is described in “Cascade Single chipphosphor-free while light emitting diodes”, Applied Physics Letters,2008 by X. Guo, G. Shen, et al. (“Guo”). It involves bonding GaAs basedred LEDs with GaN based blue-green LEDs to produce white light.Unfortunately, this bonding process requires 600° C. temperatures,causing issues with mismatch of thermal expansion co-efficients andcracking. Another publication on this topic is “A trichromaticphosphor-free white light-emitting diode by using adhesive bondingscheme”, Proc. SPIE, Vol. 7635, 2009 by D. Chuai, X. Guo, et al.(“Chuai”). It involves bonding red LEDs with green-blue LED stacks.Bonding is done at the die level after dicing, which is more costly thana wafer-based approach.

U.S. patent application Ser. No. 12/130,824 describes various stackedRGB LED devices. It also briefly mentions a method for construction of astacked LED where all layers of the stacked LED are transferred usinglift-off with a temporary carrier and Indium Tin Oxide (ITO) tosemiconductor bonding. This method has several issues for constructing aRGB LED stack. First, it is difficult to manufacture a lift-off with atemporary carrier of red LEDs for producing a RGB LED stack, especiallyfor substrates larger than 2 inch. This is because red LEDs aretypically constructed on non-transparent GaAs substrates, and lift-offwith a temporary carrier is done by using an epitaxial lift-off process.Here, the thin film to be transferred typically sits atop a“release-layer” (eg. AlAs), this release layer is removed by etchprocedures after the thin film is attached to a temporary substrate.Scaling this process to 4 inch wafers and bigger is difficult. Second,it is very difficult to perform the bonding of ITO to semiconductormaterials of a LED layer at reasonable temperatures, as described in thepatent application Ser. No. 12/130,824.

It is therefore clear that a better method for constructing RGB LEDswill be helpful. Since RGB LEDs are significantly more efficient thanpcLEDs, they can be used as replacements of today's phosphor-based LEDsfor many applications, provided a cheap and effective method ofconstructing RGB LEDs can be invented.

Background on Image-Sensors:

Image sensors are used in applications such as cameras. Red, blue, andgreen components of the incident light are sensed and stored in digitalformat. CMOS image sensors typically contain a photodetector and sensingcircuitry. Almost all image sensors today have both the photodetectorand sensing circuitry on the same chip. Since the area consumed by thesensing circuits is high, the photodetector cannot see the entireincident light, and image capture is not as efficient.

To tackle this problem, several researchers have proposed building thephotodetectors and the sensing circuitry on separate chips and stackingthem on top of each other. A publication that describes this method is“Megapixel CMOS image sensor fabricated in three-dimensional integratedcircuit technology”, Intl. Solid State Circuits Conference 2005 bySuntharalingam, V., Berger, R., et al. (“Suntharalingam”). Theseproposals use through-silicon via (TSV) technology where alignment isdone in conjunction with bonding. However, pixel size is reaching the 1μm range, and successfully processing TSVs in the 1 μm range or below isvery difficult. This is due to alignment issues while bonding. Forexample, the International Technology Roadmap for Semiconductors (ITRS)suggests that the 2-4 um TSV pitch will be the industry standard until2012. A 2-4 μm pitch TSV will be too big for a sub-1 μm pixel.Therefore, novel techniques of stacking photodetectors and sensingcircuitry are required.

A possible solution to this problem is given in “Setting up 3DSequential Integration for Back-Illuminated CMOS Image Sensors withHighly Miniaturized Pixels with Low Temperature Fully-depleted SOITransistors,” IEDM, p. 1-4 (2008) by P. Coudrain et al. (“Coudrain”). Inthe publication, transistors are monolithically integrated on top ofphotodetectors. Unfortunately, transistor process temperatures reach600° C. or more. This is not ideal for transistors (that require ahigher thermal budget) and photodetectors (that may prefer a lowerthermal budget).

Background on Displays:

Liquid Crystal Displays (LCDs) can be classified into two types based onmanufacturing technology utilized: (1) Large-size displays that are madeof amorphous/polycrystalline silicon thin-film-transistors (TFTs), and(2) Microdisplays that utilize single-crystal silicon transistors.Microdisplays are typically used where very high resolution is needed,such as camera/camcorder view-finders, projectors and wearablecomputers.

Microdisplays are made in semiconductor fabs with 200 mm or 300 mmwafers. They are typically constructed with LCOS(Liquid-Crystal-on-Silicon) Technology and are reflective in nature. Anexception to this trend of reflective microdisplays is technology fromKopin Corporation (U.S. Pat. No. 5,317,236, filed December 1991). Thiscompany utilizes transmittive displays with a lift-off layer transferscheme. Transmittive displays may be generally preferred for variousapplications.

While lift-off layer transfer schemes are viable for transmittivedisplays, they are frequently not used for semiconductor manufacturingdue to yield issues. Therefore, other layer transfer schemes will behelpful. However, it is not easy to utilize other layer transfer schemesfor making transistors in microdisplays. For example, application of“smart-cut” layer transfer to attach monocrystalline silicon transistorsto glass is described in “Integration of Single Crystal Si TFTs andCircuits on a Large Glass Substrate”, IEDM 2009 by Y. Takafuji, Y.Fukushima, K. Tomiyasu, et al. (“Takafuji”). Unfortunately, hydrogen isimplanted through the gate oxide of transferred transistors in theprocess, and this degrades performance. Process temperatures are as highas 600° C. in this paper, and this requires costly glass substrates.Several challenges therefore need to be overcome for efficient layertransfer, and require innovation.

Background on Solar Cells:

Solar cells can be constructed of several materials such as, forexample, silicon and compound semiconductors. The highest efficiencysolar cells are typically multi-junction solar cells that areconstructed of compound semiconductor materials. These multi-junctionsolar cells are typically constructed on a germanium substrate, andsemiconductors with various band-gaps are epitaxially grown atop thissubstrate to capture different portions of the solar spectrum.

There are a few issues with standard multi-junction solar cells. Sincemultiple junctions are grown epitaxially above a single substrate (suchas Germanium) at high temperature, materials used for differentjunctions are restricted to those that have lattice constants andthermal expansion co-efficients close to those of the substrate.Therefore, the choice of materials used to build junctions formulti-junction solar cells is limited. As a result, most multi-junctionsolar cells commercially available today cannot capture the full solarspectrum. Efficiency of the solar cell can be improved if a large bandof the solar spectrum is captured. Furthermore, multi-junction solarcells today suffer from high cost of the substrate above which multiplejunctions are epitaxially grown. Methods to build multi-junction solarcells that tackle both these issues will be helpful.

A method of making multi-junction solar cells by mechanically bondingtwo solar cells, one with a Germanium junction and another with acompound semiconductor junction is described in “Towards highlyefficient 4-terminal mechanical photovoltaic stacks”, III-Vs Review,Volume 19, Issue 7, September-October 2006 by Giovanni Flamand, JefPoortmans (“Flamand”). In this work, the authors make the compoundsemiconductor junctions on a Germanium substrate epitaxially. They thenetch away the entire Germanium substrate after bonding to the othersubstrate with the Germanium junction. The process uses two Germaniumsubstrates, and is therefore expensive.

Techniques to create multi-junction solar cells with layer transfer havebeen described in “Wafer bonding and layer transfer processes for4-junction high efficiency solar cells,” Photovoltaic SpecialistsConference, 2002. Conference Record of the Twenty-Ninth IEEE, vol., no.,pp. 1039-1042, 19-24 May 2002 by Zahler, J. M.; Fontcuberta i Morral,A.; Chang-Geun Ahn; Atwater, H. A.; Wanlass, M. W.; Chu, C. and Iles, P.A. An anneal is used for ion-cut purposes, and this anneal is typicallydone at temperatures higher than 350-400° C. (if high bond strength isdesired). When that happens, cracking and defects can be produced due tomismatch of co-efficients of thermal expansion between various layers inthe stack. Furthermore, semiconductor layers are bonded together, andthe quality of this bond not as good as oxide-to-oxide bonding,especially for lower process temperatures.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will be understood andappreciated more fully from the following detailed description, taken inconjunction with the drawings in which:

FIGS. 1A-B illustrate red, green and blue type LEDs (prior art).

FIG. 2 illustrates a conventional RGB LED where red, green, and blueLEDs are placed side-by-side (prior art).

FIG. 3 illustrates a prior-art phosphor-based LED (pcLED).

FIGS. 4A-S illustrate an embodiment of this invention, where RGB LEDsare stacked with ion-cut technology, flip-chip packaging and conductiveoxide bonding.

FIGS. 5A-Q illustrate an embodiment of this invention, where RGB LEDsare stacked with ion-cut technology, wire bond packaging and conductiveoxide bonding.

FIGS. 6A-L illustrate an embodiment of this invention, where stacked RGBLEDs are formed with ion-cut technology, flip-chip packaging and alignedbonding.

FIGS. 7A-L illustrate an embodiment of this invention, where stacked RGBLEDs are formed with laser lift-off, substrate etch, flip-chip packagingand conductive oxide bonding.

FIGS. 8A-B illustrate an embodiment of this invention, where stacked RGBLEDs are formed from a wafer having red LED layers and another waferhaving both green and blue LED layers.

FIG. 9 illustrates an embodiment of this invention, where stacked RGBLEDs are formed with control and driver circuits for the LED built onthe silicon sub-mount.

FIG. 10 illustrates an embodiment of this invention, where stacked RGBLEDs are formed with control and driver circuits as well as imagesensors for the LED built on the silicon sub-mount.

FIGS. 11A-F is a prior art illustration of pcLEDs constructed withion-cut processes.

FIGS. 12A-F illustrate an embodiment of this invention, where pcLEDs areconstructed with ion-cut processes.

FIG. 13 illustrates a prior art image sensor stacking technology whereconnections between chips are aligned during bonding.

FIG. 14 describes two configurations for stacking photodetectors andread-out circuits.

FIGS. 15A-H illustrate an embodiment of this invention, where a CMOSimage sensor is formed by stacking a photodetector monolithically on topof read-out circuits using ion-cut technology.

FIG. 16 illustrates the absorption process of different wavelengths oflight at different depths in silicon image sensors.

FIGS. 17A-B illustrate an embodiment of this invention, where red, greenand blue photodetectors are stacked monolithically atop read-outcircuits using ion-cut technology (for an image sensor).

FIGS. 18A-B illustrate an embodiment of this invention, where red, greenand blue photodetectors are stacked monolithically atop read-outcircuits using ion-cut technology for a different configuration (for animage sensor).

FIGS. 19A-B illustrate an embodiment of this invention, where an imagesensor that can detect both visible and infra-red light without any lossof resolution is constructed.

FIG. 20A illustrates an embodiment of this invention, where polarizationof incoming light is detected.

FIG. 20B illustrates another embodiment of this invention, where animage sensor with high dynamic range is constructed.

FIG. 21 illustrates an embodiment of this invention, where read-outcircuits are constructed monolithically above photodetectors in an imagesensor.

FIGS. 22A-G illustrate an embodiment of this invention, where a displayis constructed using sub-400° C. processed single crystal siliconrecessed channel transistors on a glass substrate.

FIGS. 23A-H illustrate an embodiment of this invention, where a displayis constructed using sub-400° C. processed single crystal siliconreplacement gate transistors on a glass substrate.

FIGS. 24A-F illustrate an embodiment of this invention, where a displayis constructed using sub-400° C. processed single crystal junctionlesstransistors on a glass substrate.

FIGS. 25A-D illustrate an embodiment of this invention, where a displayis constructed using sub-400° C. processed amorphous silicon orpolysilicon junctionless transistors on a glass substrate.

FIGS. 26A-C illustrate an embodiment of this invention, where amicrodisplay is constructed using stacked RGB LEDs and control circuitsare connected to each pixel with solder bumps.

FIGS. 27A-D illustrate an embodiment of this invention, where amicrodisplay is constructed using stacked RGB LEDs and control circuitsare monolithically stacked above the LED.

FIGS. 28A-C illustrate a description of multijunction solar cells (priorart).

FIGS. 29A-H illustrate an embodiment of this invention, wheremultijunction solar cells are constructed using sub-250° C. bond andcleave processes.

FIGS. 30A-D illustrate an embodiment of this invention, where afull-spectrum multi-junction solar cells is constructed using sub-250°C. bond and cleave processes.

DETAILED DESCRIPTION

Embodiments of the present invention are now described with reference toFIGS. 1-30, it being appreciated that the figures illustrate the subjectmatter not to scale or to measure.

NuLED Technology:

FIG. 1A illustrates a cross-section of prior art red LEDs. Red LEDs aretypically constructed on a Gallium Arsenide substrate 100.Alternatively, Gallium Phosphide or some other material can be used forthe substrate. Since Gallium Arsenide 100 is opaque, a Bragg Reflector101 is added to ensure light moves in the upward direction. Red light isproduced by a p-n junction with multiple quantum wells (MQW). A p-typeconfinement layer 104, a n-type confinement layer 102 and a multiplequantum well 103 form this part of the device. A current spreadingregion 105 ensures current flows throughout the whole device and notjust close to the contacts. Indium Tin Oxide (ITO) could be used for thecurrent spreading region 105. A top contact 106 and a bottom contact 107are used for making connections to the LED. It will be obvious to oneskilled in the art based on the present disclosure that manyconfigurations and material combinations for making red LEDs arepossible. This invention is not limited to one particular configurationor set of materials.

FIG. 1B also illustrates green and blue LED cross-sections. These aretypically constructed on a sapphire, SiC or bulk-GaN substrate,indicated by 108. Light is produced by a p-n junction with multiplequantum wells made of In_(x)Ga_(1-x)N/GaN. A p-type confinement layer111, a n-type confinement layer 109 and a multiple quantum well 110 formthis part of the device. The value of subscript x in In_(x)Ga_(1-x)Ndetermines whether blue light or green light is produced. For example,blue light typically corresponds to x ranging from 10% to 20% whilegreen light typically corresponds to x ranging from 20% to 30%. Acurrent spreader 112 is typically used as well. ITO could be a materialused for the current spreader 112. An alternative material for currentspreading could be ZnO. A top contact 113 and a bottom contact 114 areused for making connections to the LED. It will be obvious to oneskilled in the art based on the present disclosure that manyconfigurations and material combinations for making blue and green LEDsare possible. This invention is not limited to one particularconfiguration or set of materials.

White LEDs for various applications can be constructed in two ways.Method 1 is described in FIG. 2 which shows Red LED 201, blue LED 202,and green LED 203 that are constructed separately and placedside-by-side. Red light 204, blue light 205 and green light 206 aremixed to form white light 207. While these “RGB LEDs” are efficient,they suffer from cost issues and have problems related to light mixing.Method 2 is described in FIG. 3 which shows a blue LED 301 constructedand coated with a phosphor layer 302. The yellow phosphor layer convertsblue light into white light 303. These “Phosphor-based LEDs” or “pcLEDs”are cheaper than RGB LEDs but are typically not as efficient.

FIG. 4A-S illustrate an embodiment of this invention where Red, Blue,and Green LEDs are stacked on top of each other with smart layertransfer techniques. A smart layer transfer may be defined as one ormore of the following processes:

-   -   Ion-cut, variations of which are referred to as smart-cut,        nano-cleave and smart-cleave: Further information on ion-cut        technology is given in “Frontiers of silicon-on-insulator,” J.        Appl. Phys. 93, 4955-4978 (2003) by G. K. Celler and S.        Cristolovean (“Celler”) and also in “Mechanically induced Si        layer transfer in hydrogen-implanted Si wafers,” Appl. Phys.        Lett., vol. 76, pp. 2370-2372, 2000 by K. Henttinen, I. Suni,        and S. S. Lau (“Hentinnen”).    -   Porous silicon approaches such as ELTRAN: These are described in        “Eltran, Novel SOI Wafer Technology,” JSAP International, Number        4, July 2001 by T. Yonehara and K. Sakaguchi (“Yonehara”).    -   Bonding a substrate with single crystal layers followed by        Polishing, Time-controlled etch-back or Etch-stop layer        controlled etch-back to thin the bonded substrate: These are        described in U.S. Pat. No. 6,806,171 by A. Ulyashin and A.        Usenko (“Ulyashin”) and “Enabling SOI-Based Assembly Technology        for Three-Dimensional (3D) Integrated Circuits (ICs),” IEDM        Tech. Digest, p. 363 (2005) by A. W. Topol, D. C. La Tulipe, L.        Shi, S. M. Alam, D. J. Frank, S. E. Steen, J. Vichiconti, D.        Posillico, M. Cobb, S. Medd, J. Patel, S. Goma, D.        DiMilia, M. T. Robson, E. Duch, M. Farinelli, C. Wang, R. A.        Conti, D. M. Canaperi, L. Deligianni, A. Kumar, K. T.        Kwietniak, C. D'Emic, J. Ott, A. M. Young, K. W. Guarini, and M.        Ieong (“Topol”).    -   Bonding a wafer with a Gallium Nitride film epitaxially grown on        a sapphire substrate followed by laser lift-off for removing the        transparent sapphire substrate: This method may be suitable for        deposition of Gallium Nitride thin films, and is described in        U.S. Pat. No. 6,071,795 by Nathan W. Cheung, Timothy D. Sands        and William S. Wong (“Cheung”).    -   Rubber stamp layer transfer: This is described in “Solar cells        sliced and diced,” 19 May 2010, Nature News.

This process of constructing RGB LEDs could include several steps thatoccur in a sequence from Step (A) to Step (S). Many of them share commoncharacteristics, features, modes of operation, etc. When the samereference numbers are used in different drawing figures, they are usedto indicate analogous, similar or identical structures to enhance theunderstanding of the present invention by clarifying the relationshipsbetween the structures and embodiments presented in the variousdiagrams—particularly in relating analogous, similar or identicalfunctionality to different physical structures.

Step (A) is illustrated in FIG. 4A. A red LED wafer 436 is constructedon a GaAs substrate 402 and includes a N-type confinement layer 404, amultiple quantum well (MQW) 406, a P-type confinement layer 408, anoptional reflector 409 and an ITO current spreader 410. Examples ofmaterials used to construct these layers, include, but are not limitedto, doped AlInGaP for the N-type confinement layer 404 and P-typeconfinement layer 408, the multiple quantum well layer 406 could be ofAlInGaP and GaInP and the optional reflector 409 could be a distributedBragg Reflector. A double heterostructure configuration or singlequantum well configuration could be used instead of a multiple quantumwell configuration. Various other material types and configurationscould be used for constructing the red LEDs for this process. Yetanother wafer is constructed with a green LED. The green LED wafer 438is constructed on a sapphire or SiC or bulk-GaN substrate 412 andincludes a N-type confinement layer 414, a multiple quantum well (MQW)416, a buffer layer 418, a P-type confinement layer 420, an optionalreflector 421 and an ITO current spreader 422. Yet another wafer isconstructed with a blue LED. The blue LED wafer 440 is constructed on asapphire or SiC or bulk-GaN substrate 424 and includes a N-typeconfinement layer 426, a multiple quantum well (MQW) 428, a buffer layer430, a P-type confinement layer 432, an optional reflector 433 and anITO current spreader 434. Examples of materials used to construct theseblue and green LED layers, include, but are not limited to, doped GaNfor the N-type and P-type confinement layers 414, 420, 426 and 432,AlGaN for the buffer layers 430 and 418 and InGaN/GaN for the multiplequantum wells 416 and 428. The optional reflectors 421 and 433 could bedistributed Bragg Reflectors or some other type of reflectors. Variousother material types and configurations could be used for constructingblue and green LEDs for this process.Step (B) is illustrated in FIG. 4B. The blue LED wafer 440 from FIG. 4Ais used for this step. Various elements in FIG. 4B such as, for example,424, 426, 428, 430, 432, 433, and 434 have been previously described.Hydrogen is implanted into the wafer at a certain depth indicated bydotted lines 442. Alternatively, helium could be used for this step.Step (C) is illustrated in FIG. 4C. A glass substrate 446 is taken andan ITO layer 444 is deposited atop it.Step (D) is illustrated in FIG. 4D. The wafer shown in FIG. 4B isflipped and bonded atop the wafer shown in FIG. 4C using ITO-ITObonding. Various elements in FIG. 4D such as 424, 426, 428, 430, 432,433, 434, 442, 446, and 444 have been previously described. The ITOlayer 444 is essentially bonded to the ITO layer 434 using anoxide-to-oxide bonding process.Step (E) is illustrated in FIG. 4E. Various elements in FIG. 4E such as424, 426, 428, 430, 432, 433, 434, 442, 446, and 444 have beenpreviously described. An ion-cut process is conducted to cleave thestructure shown in FIG. 4D at the hydrogen implant plane 442. Thision-cut process may use a mechanical cleave. An anneal process could beutilized for the cleave as well. After the cleave, a chemical mechanicalpolish (CMP) process is conducted to planarize the surface. The N-typeconfinement layer present after this cleave and CMP process is indicatedas 427.Step (F) is illustrated in FIG. 4F. Various elements in FIG. 4F such as446, 444, 434, 433, 432, 430, 428, and 427 have been previouslydescribed. An ITO layer 448 is deposited atop the N-type confinementlayer 427.Step (G) is illustrated in FIG. 4G. The green LED wafer 438 shown inStep (A) is used for this step. Various elements in FIG. 4G such as 412,414, 416, 418, 420, 421, and 422 have been described previously.Hydrogen is implanted into the wafer at a certain depth indicated bydotted lines 450. Alternatively, helium could be used for this step.Step (H) is illustrated in FIG. 4H. The structure shown in FIG. 4G isflipped and bonded atop the structure shown in FIG. 4F using ITO-ITObonding. Various elements in FIG. 4H such as 446, 444, 434, 433, 432,430, 428, 427, 448, 412, 414, 416, 418, 420, 421, 422, and 450 have beendescribed previously.Step (I) is illustrated in FIG. 41. The structure shown in FIG. 4H iscleaved at the hydrogen plane indicated by 450. This cleave process maybe preferably done with a mechanical force. Alternatively, an annealcould be used. A CMP process is conducted to planarize the surface.Various elements in FIG. 41 such as 446, 444, 434, 433, 432, 430, 428,427, 448, 416, 418, 420, 421, and 422 have been described previously.The N-type confinement layer present after this cleave and CMP processis indicated as 415.Step (J) is illustrated in FIG. 4J. An ITO layer 452 is deposited atopthe structure shown in FIG. 41. Various elements in FIG. 4J such as 446,444, 434, 433, 432, 430, 428, 427, 448, 416, 418, 420, 421, 415, and 422have been described previously.Step (K) is illustrated in FIG. 4K. The red LED wafer 436 shown in Step(A) is used for this step. Various elements in FIG. 4K such as 402, 404,406, 408, 409, and 410 have been described previously. Hydrogen isimplanted into the wafer at a certain depth indicated by dotted lines454. Alternatively, helium could be used for this step.Step (L) is illustrated in FIG. 4L. The structure shown in FIG. 4K isflipped and bonded atop the structure shown in FIG. 4J using ITO-ITObonding. Various elements in FIG. 4L such as 446, 444, 434, 433, 432,430, 428, 427, 448, 416, 418, 420, 421, 415, 422, 452, 402, 404, 406,408, 409, 410, and 454 have been described previously.Step (M) is illustrated in FIG. 4M. The structure shown in FIG. 4L iscleaved at the hydrogen plane 454. A mechanical force could be used forthis cleave. Alternatively, an anneal could be used. A CMP process isthen conducted to planarize the surface. The N-type confinement layerpresent after this process is indicated as 405. Various elements in FIG.4M such as 446, 444, 434, 433, 432, 430, 428, 427, 448, 416, 418, 420,421, 415, 422, 452, 406, 408, 409, and 410 have been describedpreviously.Step (N) is illustrated in FIG. 4N. An ITO layer 456 is deposited atopthe structure shown in FIG. 4M. Various elements in FIG. 4M such as 446,444, 434, 433, 432, 430, 428, 427, 448, 416, 418, 420, 421, 415, 422,452, 406, 408, 409, 410, and 405 have been described previously.Step (O) is illustrated in FIG. 40. A reflecting material layer 458,constructed for example with Aluminum or Silver, is deposited atop thestructure shown in FIG. 4N. Various elements in FIG. 40 such as 446,444, 434, 433, 432, 430, 428, 427, 448, 416, 418, 420, 421, 415, 422,452, 406, 408, 409, 410, 456, and 405 have been described previously.Step (P) is illustrated in FIG. 4P. The process of making contacts tovarious layers and packaging begins with this step. A contact andbonding process similar to the one used in “High-power AlGaInN flip-chiplight-emitting diodes,” Applied Physics Letters, vol. 78, no. 22, pp.3379-3381, May 2001, by Wierer, J. J.; Steigerwald, D. A.; Krames, M.R.; OShea, J. J.; Ludowise, M. J.; Christenson, G.; Shen, Y.-C.; Lowery,C.; Martin, P. S.; Subramanya, S.; Gotz, W.; Gardner, N. F.; Kern, R.S.; Stockman, S. A. is used. Vias 460 are etched to different layers ofthe LED stack. Various elements in FIG. 4P such as 446, 444, 434, 433,432, 430, 428, 427, 448, 416, 418, 420, 421, 415, 422, 452, 406, 408,409, 410, 456, 405, and 458 have been described previously. After thevia holes 460 are etched, they may optionally be filled with an oxidelayer and polished with CMP. This fill with oxide may be optional, andthe preferred process may be to leave the via holes as such withoutfill. Note that the term contact holes could be used instead of the termvia holes. Similarly, the term contacts could be used instead of theterm vias.Step (Q) is illustrated in FIG. 4Q. Aluminum is deposited to fill viaholes 460 from FIG. 4P. Following this deposition, a lithography andetch process is utilized to define the aluminum metal to form vias 462.The vias 462 are smaller in diameter than the via holes 460 shown inFIG. 4P. Various elements in FIG. 4Q such as 446, 444, 434, 433, 432,430, 428, 427, 448, 416, 418, 420, 421, 415, 422, 452, 406, 408, 409,410, 456, 405, 460, and 458 have been described previously.Step (R) is illustrated in FIG. 4R. A nickel layer 464 and a solderlayer 466 are formed using standard procedures. Various elements in FIG.4R such as 446, 444, 434, 433, 432, 430, 428, 427, 448, 416, 418, 420,421, 415, 422, 452, 406, 408, 409, 410, 456, 405, 460, 462, and 458 havebeen described previously.Step (S) is illustrated in FIG. 4S. The solder layer 466 is then bondedto pads on a silicon sub-mount 468. Various elements in FIG. 4S such as446, 444, 434, 433, 432, 430, 428, 427, 448, 416, 418, 420, 421, 415,422, 452, 406, 408, 409, 410, 456, 405, 460, 462, 458, 464, and 466 havebeen described previously. The configuration of optional reflectors 433,421, and 409 determines light output coming from the LED. A preferredembodiment of this invention may not have a reflector 433, and may havethe reflector 421 (reflecting only the blue light produced by multiplequantum well 428) and the reflector 409 (reflecting only the green lightproduced by multiple quantum well 416). In the process described in FIG.4A-FIG. 4S, the original substrates in FIG. 4A, namely 402, 412 and 424,can be reused after ion-cut. This reuse may make the process morecost-effective.

FIGS. 5A-Q describe an embodiment of this invention, where RGB LEDs arestacked with ion-cut technology, wire bond packaging and conductiveoxide bonding. Essentially, smart-layer transfer is utilized toconstruct this embodiment of the invention. This process of constructingRGB LEDs could include several steps that occur in a sequence from Step(A) to Step (Q). Many of the steps share common characteristics,features, modes of operation, etc. When the same reference numbers areused in different drawing figures, they are used to indicate analogous,similar or identical structures to enhance the understanding of thepresent invention by clarifying the relationships between the structuresand embodiments presented in the various diagrams—particularly inrelating analogous, similar or identical functionality to differentphysical structures.

Step (A): This is illustrated using FIG. 5A. A red LED wafer 536 isconstructed on a GaAs substrate 502 and includes a N-type confinementlayer 504, a multiple quantum well (MQW) 506, a P-type confinement layer508, an optional reflector 509 and an ITO current spreader 510. Examplesof materials used to construct these layers, include, but are notlimited to, doped AlInGaP for the N-type confinement layer 504 andP-type confinement layer 508, the multiple quantum well layer 506 couldbe of AlInGaP and GaInP and the optional reflector 509 could be adistributed Bragg Reflector. A double heterostructure configuration orsingle quantum well configuration could be used instead of a multiplequantum well configuration. Various other material types andconfigurations could be used for constructing the red LEDs for thisprocess. Yet another wafer is constructed with a green LED. The greenLED wafer 538 is constructed on a sapphire or SiC or bulk-GaN substrate512 and includes a N-type confinement layer 514, a multiple quantum well(MQW) 516, a buffer layer 518, a P-type confinement layer 520, anoptional reflector 521 and an ITO current spreader 522. Yet anotherwafer is constructed with a blue LED. The blue LED wafer 540 isconstructed on a sapphire or SiC or bulk-GaN substrate 524 and includesa N-type confinement layer 526, a multiple quantum well (MQW) 528, abuffer layer 530, a P-type confinement layer 532, an optional reflector533 and an ITO current spreader 534. Examples of materials used toconstruct these blue and green LED layers, include, but are not limitedto, doped GaN (for the N-type and P-type confinement layers 514, 520,526, and 532), AlGaN (for the buffer layers 530 and 518), and InGaN/GaN(for the multiple quantum wells 516 and 528). The optional reflectors521 and 533 could be distributed Bragg Reflectors or some other type ofreflectors. Various other material types and configurations could beused for constructing blue and green LEDs for this process.Step (B) is illustrated in FIG. 5B. The red LED wafer 536 from FIG. 5Ais used for this step. Various elements in FIG. 5B such as 502, 504,506, 508, 509, and 510 have been previously described. Hydrogen isimplanted into the wafer at a certain depth indicated by dotted lines542. Alternatively, helium could be used for this step.Step (C) is illustrated in FIG. 5C. A silicon substrate 546 is taken andan ITO layer 544 is deposited atop it.Step (D) is illustrated in FIG. 5D. The wafer shown in FIG. 5B isflipped and bonded atop the wafer shown in FIG. 5C using ITO-ITObonding. Various elements in FIG. 5D such as 502, 504, 506, 508, 509,510, 542, 544, and 546 have been previously described. The ITO layer 544is essentially bonded to the ITO layer 510 using an oxide-to-oxidebonding process.Step (E) is illustrated in FIG. 5E. Various elements in FIG. 5E such as506, 508, 509, 510, 544 and 546 have been previously described. Anion-cut process is conducted to cleave the structure shown in FIG. 5D atthe hydrogen implant plane 542. This ion-cut process could preferablyuse a mechanical cleave. An anneal process could be utilized for thecleave as well. After the cleave, a chemical mechanical polish (CMP)process is conducted to planarize the surface. The N-type confinementlayer present after this cleave and CMP process is indicated as 505.Step (F) is illustrated in FIG. 5F. Various elements in FIG. 5F such as505, 506, 508, 509, 510, 544, and 546 have been previously described. AnITO layer 548 is deposited atop the N-type confinement layer 505.Step (G) is illustrated in FIG. 5G. The green LED wafer 538 shown inStep (A) is used for this step. Various elements in FIG. 5G such as 512,514, 516, 518, 520, 521, and 522 have been described previously.Hydrogen is implanted into the wafer at a certain depth indicated bydotted lines 550. Alternatively, helium could be used for this step.Step (H) is illustrated in FIG. 5H. The structure shown in FIG. 5G isflipped and bonded atop the structure shown in FIG. 5F using ITO-ITObonding. Various elements in FIG. 5H such as 505, 506, 508, 509, 510,544, 546, 548, 512, 514, 516, 518, 520, 521, 550, and 522 have beendescribed previously.Step (I) is illustrated in FIG. 5I. The structure shown in FIG. 5H iscleaved at the hydrogen plane indicated by 550. This cleave process maybe preferably done with a mechanical force. Alternatively, an annealcould be used. A CMP process is conducted to planarize the surface.Various elements in FIG. 51 such as 505, 506, 508, 509, 510, 544, 546,548, 516, 518, 520, 521, and 522 have been described previously. TheN-type confinement layer present after this cleave and CMP process isindicated as 515.Step (J) is illustrated using FIG. 51. An ITO layer 552 is depositedatop the structure shown in FIG. 5I. Various elements in FIG. 51 such as505, 506, 508, 509, 510, 544, 546, 548, 516, 518, 520, 521, 515, and 522have been described previously.Step (K) is illustrated using FIG. 5K. The blue LED wafer 540 from FIG.5A is used for this step. Various elements in FIG. 5K such as 524, 526,528, 530, 532, 533, and 534 have been previously described. Hydrogen isimplanted into the wafer at a certain depth indicated by dotted lines554. Alternatively, helium could be used for this step.Step (L) is illustrated in FIG. 5L. The structure shown in FIG. 5K isflipped and bonded atop the structure shown in FIG. 5J using ITO-ITObonding. Various elements in FIG. 4L such as 505, 506, 508, 509, 510,544, 546, 548, 516, 518, 520, 521, 515, 522, 552, 524, 526, 528, 530,532, 533, 554, and 534 have been described previously.Step (M) is illustrated in FIG. 5M. The structure shown in FIG. 5L iscleaved at the hydrogen plane 554. A mechanical force could be used forthis cleave. Alternatively, an anneal could be used. A CMP process isthen conducted to planarize the surface. The N-type confinement layerpresent after this process is indicated as 527. Various elements in FIG.5M such as 505, 506, 508, 509, 510, 544, 546, 548, 516, 518, 520, 521,515, 522, 552, 528, 530, 532, 533, and 534 have been describedpreviously.Step (N) is illustrated in FIG. 5N. An ITO layer 556 is deposited atopthe structure shown in FIG. 5M. Various elements in FIG. 5N such as 505,506, 508, 509, 510, 544, 546, 548, 516, 518, 520, 521, 515, 522, 552,528, 530, 532, 533, and 534 have been described previously.Step (O) is illustrated in FIG. 50. The process of making contacts tovarious layers and packaging begins with this step. Various elements inFIG. 50 such as 505, 506, 508, 509, 510, 544, 546, 548, 516, 518, 520,521, 515, 522, 552, 528, 530, 532, 533, 556, and 534 have been describedpreviously. Via holes 560 are etched to different layers of the LEDstack. After the via holes 560 are etched, they may optionally be filledwith an oxide layer and polished with CMP. This fill with oxide may beoptional, and the preferred process may be to leave the via holes assuch without fill.Step (P) is illustrated in FIG. 5P. Aluminum is deposited to fill viaholes 560 from FIG. 50. Following this deposition, a lithography andetch process is utilized to define the aluminum metal to form via holes562. Various elements in FIG. 5P such as 505, 506, 508, 509, 510, 544,546, 548, 516, 518, 520, 521, 515, 522, 552, 528, 530, 532, 533, 556,560, and 534 have been described previously.Step (Q) is illustrated in FIG. 5Q. Bond pads 564 are constructed andwire bonds are attached to these bond pads following this step. Variouselements in FIG. 5Q such as 505, 506, 508, 509, 510, 544, 546, 548, 516,518, 520, 521, 515, 522, 552, 528, 530, 532, 533, 556, 560, 562, and 534have been described previously. The configuration of optional reflectors533, 521 and 509 determines light output coming from the LED. Thepreferred embodiment of this invention is to have reflector 533 reflectonly blue light produced by multiple quantum well 528, to have thereflector 521 reflecting only green light produced by multiple quantumwell 516 and to have the reflector 509 reflect light produced bymultiple quantum well 506. In the process described in FIG. 5A-FIG. 5Q,the original substrates in FIG. 5A, namely 502, 512 and 524, can bere-used after ion-cut. This may make the process more cost-effective.

FIGS. 6A-L show an alternative embodiment of this invention, wherestacked RGB LEDs are formed with ion-cut technology, flip-chip packagingand aligned bonding. A smart layer transfer process, ion-cut, istherefore utilized. This process of constructing RGB LEDs could includeseveral steps that occur in a sequence from Step (A) to Step (K). Manyof the steps share common characteristics, features, modes of operation,etc. When identical reference numbers are used in different drawingfigures, they are used to indicate analogous, similar or identicalstructures to enhance the understanding of the present invention byclarifying the relationships between the structures and embodimentspresented in the various diagrams—particularly in relating analogous,similar or identical functionality to different physical structures.

Step (A) is illustrated in FIG. 6A. A red LED wafer 636 is constructedon a GaAs substrate 602 and includes a N-type confinement layer 604, amultiple quantum well (MQW) 606, a P-type confinement layer 608, anoptional reflector 609 and an ITO current spreader 610. Above the ITOcurrent spreader 610, a layer of silicon oxide 692 is deposited,patterned, etched and filled with a metal 690 (e.g., tungsten) which isthen CMPed. Examples of materials used to construct these layers,include, but are not limited to, doped AlInGaP for the N-typeconfinement layer 604 and P-type confinement layer 608, the multiplequantum well layer 606 could be of AlInGaP and GaInP and the optionalreflector 609 could be a distributed Bragg Reflector. A doubleheterostructure configuration or single quantum well configuration couldbe used instead of a multiple quantum well configuration. Various othermaterial types and configurations could be used for constructing the redLEDs for this process. Yet another wafer is constructed with a greenLED. The green LED wafer 638 is constructed on a sapphire or SiC orbulk-GaN substrate 612 and includes a N-type confinement layer 614, amultiple quantum well (MQW) 616, a buffer layer 618, a P-typeconfinement layer 620, an optional reflector 621 and an ITO currentspreader 622. Above the ITO current spreader 622, a layer of siliconoxide 696 is deposited, patterned, etched and filled with a metal 694(e.g., tungsten) which is then CMPed. Yet another wafer is constructedwith a blue LED. The blue LED wafer 640 is constructed on a sapphire orSiC or bulk-GaN substrate 624 and includes a N-type confinement layer626, a multiple quantum well (MQW) 628, a buffer layer 630, a P-typeconfinement layer 632, an optional reflector 633 and an ITO currentspreader 634. Above the ITO current spreader 634, a layer of silicondioxide 698 is deposited. Examples of materials used to construct theseblue and green LED layers, include, but are not limited to, doped GaNfor the N-type and P-type confinement layers 614, 620, 626 and 632,AlGaN for the buffer layers 630 and 618 and InGaN/GaN for the multiplequantum wells 616 and 628. The optional reflectors 621 and 633 could bedistributed Bragg Reflectors or some other type of reflectors. Variousother material types and configurations could be used for constructingblue and green LEDs for this process.Step (B) is illustrated in FIG. 6B. The blue LED wafer 640 from FIG. 6Ais used for this step. Various elements in FIG. 6B such as 624, 626,628, 630, 632, 633, 698, and 634 have been previously described.Hydrogen is implanted into the wafer at a certain depth indicated bydotted lines 642. Alternately, helium could be used for this step.Step (C) is illustrated in FIG. 6C. A glass substrate 646 is taken and asilicon dioxide layer 688 is deposited atop it.Step (D) is illustrated in FIG. 6D. The wafer shown in FIG. 6B isflipped and bonded atop the wafer shown in FIG. 6C using oxide-oxidebonding. Various elements in FIG. 6D such as 624, 626, 628, 630, 632,633, 698, 642, 646, 688, and 634 have been previously described. Theoxide layer 688 is essentially bonded to the oxide layer 698 using anoxide-to-oxide bonding process.Step (E) is illustrated in FIG. 6E. Various elements in FIG. 6E such as628, 630, 632, 633, 698, 646, 688, and 634 have been previouslydescribed. An ion-cut process is conducted to cleave the structure shownin FIG. 6D at the hydrogen implant plane 642. This ion-cut process maybe preferably using a mechanical cleave. An anneal process could beutilized for the cleave as well. After the cleave, a chemical mechanicalpolish (CMP) process is conducted to planarize the surface. The N-typeconfinement layer present after this cleave and CMP process is indicatedas 627.Step (F) is illustrated in FIG. 6F. Various elements in FIG. 6F such as628, 630, 632, 633, 698, 646, 688, 627, and 634 have been previouslydescribed. An ITO layer 648 is deposited atop the N-type confinementlayer 627. Above the ITO layer 648, a layer of silicon oxide 686 isdeposited, patterned, etched and filled with a metal 684 (e.g.,tungsten) which is then CMPed.Step (G) is illustrated in FIG. 6G. The green LED wafer 638 shown inStep (A) is used for this step. Various elements in FIG. 6G such as 612,614, 616, 618, 620, 621, 696, 694, and 622 have been describedpreviously. Hydrogen is implanted into the wafer at a certain depthindicated by dotted lines 650. Alternatively, helium could be used forthis step.Step (H) is illustrated in FIG. 6H. The structure shown in FIG. 6G isflipped and bonded atop the structure shown in FIG. 6F using oxide-oxidebonding. The metal regions 694 and 684 on the bonded wafers are alignedto each other. Various elements in FIG. 6H such as 628, 630, 632, 633,698, 646, 688, 627, 634, 648, 686, 684, 612, 614, 616, 618, 620, 621,696, 694, 650, and 622 have been described previously.Step (I) is illustrated in FIG. 61. The structure shown in FIG. 6H iscleaved at the hydrogen plane indicated by 650. This cleave process maybe preferably done with a mechanical force. Alternatively, an annealcould be used. A CMP process is conducted to planarize the surface.Various elements in FIG. 61 such as 628, 630, 632, 633, 698, 646, 688,627, 634, 648, 686, 684, 616, 618, 620, 621, 696, 694, and 622 have beendescribed previously. The N-type confinement layer present after thiscleave and CMP process is indicated as 615.Step (J) is illustrated in FIG. 6J. An ITO layer 652 is deposited atopthe structure shown in FIG. 61. Above the ITO layer 652, a layer ofsilicon oxide 682 is deposited, patterned, etched and filled with ametal 680 (e.g., tungsten) which is then CMPed. Various elements in FIG.6J such as 628, 630, 632, 633, 698, 646, 688, 627, 634, 648, 686, 684,616, 618, 620, 621, 696, 694, 615, and 622 have been describedpreviously.Step (K) is illustrated in FIG. 6K. Using procedures similar to Step(G)-Step (J), the red LED layer is transferred atop the structure shownin FIG. 6J. The N-type confinement layer after ion-cut is indicated by605. An ITO layer 656 is deposited atop the N-type confinement layer605. Various elements in FIG. 6K such as 628, 630, 632, 633, 698, 646,688, 627, 634, 648, 686, 684, 616, 618, 620, 621, 696, 694, 615, 690,692, 610, 609, 608, 606, and 622 have been described previously.Step (L) is illustrated in FIG. 6L. Using flip-chip packaging proceduressimilar to those described in FIG. 4A-FIG. 4S, the RGB LED stack shownin FIG. 6K is attached to a silicon sub-mount 668. 658 indicates areflecting material, 664 is a nickel layer, 666 represents solder bumps,670 is an aluminum via, and 672 is either an oxide layer or an air gap.Various elements in FIG. 6K such as 628, 630, 632, 633, 698, 646, 688,627, 634, 648, 686, 684, 616, 618, 620, 621, 696, 694, 615, 690, 692,610, 609, 608, 606, 605, 656, and 622 have been described previously.The configuration of optional reflectors 633, 621 and 609 determineslight output coming from the LED. A preferred embodiment of thisinvention may not have a reflector 633, but may have the reflector 621(reflecting only the blue light produced by multiple quantum well 628)and the reflector 609 (reflecting only the green light produced bymultiple quantum well 616). In the process described in FIG. 6A-FIG. 6L,the original substrates in FIG. 6A, namely 602, 612, and 624, can bere-used after ion-cut. This may make the process more cost-effective.

FIGS. 7A-L illustrate an embodiment of this invention, where stacked RGBLEDs are formed with laser lift-off, substrate etch, flip-chip packagingand conductive oxide bonding. Essentially, smart layer transfertechniques are used. This process could include several steps that occurin a sequence from Step (A) to Step (M). Many of the steps share commoncharacteristics, features, modes of operation, etc. When identicalreference numbers are used in different drawing figures, they are usedto indicate analogous, similar or identical structures to enhance theunderstanding of the present invention by clarifying the relationshipsbetween the structures and embodiments presented in the variousdiagrams—particularly in relating analogous, similar or identicalfunctionality to different physical structures.

Step (A): This is illustrated using FIG. 7A. A red LED wafer 736 isconstructed on a GaAs substrate 702 and includes a N-type confinementlayer 704, a multiple quantum well (MQW) 706, a P-type confinement layer708, an optional reflector 709 and an ITO current spreader 710. Examplesof materials used to construct these layers, include, but are notlimited to, doped AlInGaP for the N-type confinement layer 704 andP-type confinement layer 708, the multiple quantum well layer 706 couldbe of AlInGaP and GaInP and the optional reflector 409 could be adistributed Bragg Reflector. A double heterostructure configuration orsingle quantum well configuration could be used instead of a multiplequantum well configuration. Various other material types andconfigurations could be used for constructing the red LEDs for thisprocess. Yet another wafer is constructed with a green LED. The greenLED wafer 738 is constructed on a sapphire substrate 712 (or some othertransparent substrate) and includes a N-type confinement layer 714, amultiple quantum well (MQW) 716, a buffer layer 718, a P-typeconfinement layer 720, an optional reflector 721 and an ITO currentspreader 722. Yet another wafer is constructed with a blue LED. The blueLED wafer 740 is constructed on a sapphire substrate 724 (or some othertransparent substrate) and includes a N-type confinement layer 726, amultiple quantum well (MQW) 728, a buffer layer 730, a P-typeconfinement layer 732, an optional reflector 733 and an ITO currentspreader 734. Examples of materials used to construct these blue andgreen LED layers, include, but are not limited to, doped GaN for theN-type and P-type confinement layers 714, 720, 726 and 732, AlGaN forthe buffer layers 730 and 718 and InGaN/GaN for the multiple quantumwells 716 and 728. The optional reflectors 721 and 733 could bedistributed Bragg Reflectors or some other type of reflectors. Variousother material types and configurations could be used for constructingblue and green LEDs for this process.Step (B) is illustrated in FIG. 7B. A glass substrate 746 is taken andan ITO layer 744 is deposited atop it.Step (C) is illustrated in FIG. 7C. The blue LED wafer 740 shown in FIG.7A is flipped and bonded atop the wafer shown in FIG. 7B using ITO-ITObonding. Various elements in FIG. 7C such as 724, 726, 728, 730, 732,733, 734, 746, and 744 have been previously described. The ITO layer 744is essentially bonded to the ITO layer 734 using an oxide-to-oxidebonding process.Step (D) is illustrated in FIG. 7D. A laser is used to shine radiationthrough the sapphire substrate 724 of FIG. 7C and a laser lift-offprocess is conducted. The sapphire substrate 724 of FIG. 7C is removedwith the laser lift-off process. Further details of the laser lift-offprocess are described in U.S. Pat. No. 6,071,795 by Nathan W. Cheung,Timothy D. Sands and William S. Wong (“Cheung”). A CMP process isconducted to planarize the surface of the N confinement layer 727 afterlaser lift-off of the sapphire substrate. Various elements in FIG. 7Dsuch as 728, 730, 732, 733, 734, 746, and 744 have been previouslydescribed.Step (E) is illustrated in FIG. 7E. Various elements in FIG. 7E such as728, 730, 732, 733, 734, 746, 727, and 744 have been previouslydescribed. An ITO layer 748 is deposited atop the N confinement layer727.Step (F) is illustrated in FIG. 7F. The green LED wafer 738 is flippedand bonded atop the structure shown in FIG. 7E using ITO-ITO bonding oflayers 722 and 748. Various elements in FIG. 7F such as 728, 730, 732,733, 734, 746, 727, 748, 722, 721, 720, 718, 716, 714, 712 and 744 havebeen previously described.Step (G) is illustrated in FIG. 7G. A laser is used to shine radiationthrough the sapphire substrate 712 of FIG. 7F and a laser lift-offprocess is conducted. The sapphire substrate 712 of FIG. 7F is removedwith the laser lift-off process. A CMP process is conducted to planarizethe surface of the N-type confinement layer 715 after laser lift-off ofthe sapphire substrate. Various elements in FIG. 7G such as 728, 730,732, 733, 734, 746, 727, 748, 722, 721, 720, 718, 716, and 744 have beenpreviously described.Step (H) is illustrated in FIG. 7H. An ITO layer 752 is deposited atopthe N-type confinement layer 715. Various elements in FIG. 7H such as728, 730, 732, 733, 734, 746, 727, 748, 722, 721, 720, 718, 716, 715,and 744 have been previously described.Step (I) is illustrated in FIG. 71. The red LED wafer 736 from FIG. 7Ais flipped and bonded atop the structure shown in FIG. 7H using ITO-ITObonding of layers 710 and 752. Various elements in FIG. 71 such as 728,730, 732, 733, 734, 746, 727, 748, 722, 721, 720, 718, 716, 715, 752,710, 709, 708, 706, 704, 702, and 744 have been previously described.Step (J) is illustrated in FIG. 7J. The GaAs substrate 702 from FIG. 71is removed using etch and/or CMP. Following this etch and/or CMPprocess, the N-type confinement layer 704 of FIG. 71 is planarized usingCMP to form the N-type confinement layer 705. Various elements in FIG.7J such as 728, 730, 732, 733, 734, 746, 727, 748, 722, 721, 720, 718,716, 715, 752, 710, 709, 708, 706, and 744 have been previouslydescribed.Step (K) is illustrated in FIG. 7K. An ITO layer 756 is deposited atopthe N confinement layer 705 of FIG. 7J. Various elements in FIG. 7K suchas 728, 730, 732, 733, 734, 746, 727, 748, 722, 721, 720, 718, 716, 715,752, 710, 709, 708, 706, 705, and 744 have been previously described.Step (L) is illustrated in FIG. 7L. Using flip-chip packaging proceduressimilar to those described in FIG. 4A-FIG. 4S, the RGB LED stack shownin FIG. 7K is attached to a silicon sub-mount 768. 758 indicates areflecting material, 764 is a nickel layer, 766 represents solder bumps,770 is an aluminum via, and 772 is either an oxide layer or an air gap.Various elements in FIG. 7L such as 728, 730, 732, 733, 734, 746, 727,748, 722, 721, 720, 718, 716, 715, 752, 710, 709, 708, 706, 705, and 756have been described previously. The configuration of optional reflectors733, 721 and 709 determines light output coming from the LED. Thepreferred embodiment of this invention may not have a reflector 733, butmay have the reflector 721 (reflecting only the blue light produced bymultiple quantum well 728) and the reflector 709 (reflecting only thegreen light produced by multiple quantum well 716).

FIGS. 8A-B show an embodiment of this invention, where stacked RGB LEDsare formed from a wafer having red LED layers and another wafer havingboth green and blue LED layers. Therefore, a smart layer transferprocess is used to form the stacked RGB LED. FIG. 8A shows that a redLED wafer 836 and another wafer called a blue-green LED wafer 836 areused. The red LED wafer 836 is constructed on a GaAs substrate 802 andincludes a N-type confinement layer 804, a multiple quantum well (MQW)806, a P-type confinement layer 808, an optional reflector 809 and anITO current spreader 810. Examples of materials used to construct theselayers, include, but are not limited to, doped AlInGaP for the N-typeconfinement layer 804 and P-type confinement layer 808, the multiplequantum well layer 806 could be of AlInGaP and GaInP and the optionalreflector 809 could be a distributed Bragg Reflector. A doubleheterostructure configuration or single quantum well configuration couldbe used instead of a multiple quantum well configuration. Various othermaterial types and configurations could be used for constructing the redLEDs for this process. The blue-green LED wafer 838 is constructed on asapphire or bulk GaN or SiC substrate 812 (or some other transparentsubstrate) and includes a N-type confinement layer 814, a green multiplequantum well (MQW) 816, a blue multiple quantum well 817, a buffer layer818, a P-type confinement layer 820, an optional reflector 821, and anITO current spreader 822. Examples of materials used to construct theblue-green LED wafers, include, but are not limited to, doped GaN forthe N-type and P-type confinement layers 814, 820, AlGaN for the bufferlayer 818 and InGaN/GaN for the multiple quantum wells 816 and 817. Theoptional reflector 821 could be a distributed Bragg Reflector or someother type of reflector. The optional reflector 821 could alternativelybe built between the N-type confinement layer 814 or below it, and thisis valid for all LEDs discussed in the patent application. Various othermaterial types and configurations could be used for constructingblue-green LED wafers for this process. Using smart layer transferprocedures similar to those shown in FIGS. 4-FIG. 7, the stacked RGB LEDstructure shown in FIG. 8B is constructed. Various elements in FIG. 8Bsuch as 806, 808, 809, 810, 816, 817, 818, 820, 821, and 822 have beendescribed previously. 846 is a glass substrate, 844 is an ITO layer, 815is a N-type confinement layer for a blue-green LED, 852 is an ITO layer,805 is a N-type confinement layer for a red LED, 856 is an ITO layer,858 is a reflecting material such as, for example, silver or aluminum,864 is a nickel layer, 866 is a solder layer, 862 is a contact layerconstructed of aluminum or some other metal, 860 may be preferably anair gap but could be an oxide layer and 868 is a silicon sub-mount. Theconfiguration of optional reflectors 821 and 809 determines lightproduced by the LED. For the configuration shown in FIG. 8B, thepreferred embodiment may not have the optional reflector 821 and mayhave the optional reflector 809 reflecting light produced by the blueand green quantum wells 816 and 817.

FIG. 9 illustrates an embodiment of this invention, where stacked RGBLEDs are formed with control and driver circuits for the LED built onthe silicon sub-mount. Procedures similar to those described in FIGS.4-FIG. 7 are utilized for constructing and packaging the LED. Controland driver circuits are integrated on the silicon sub-mount 968 and canbe used for controlling and driving the stacked RGB LED. 946 is a glasssubstrate, 944 and 934 are ITO layers, 933 is an optional reflector, 932is a P-type confinement layer for a blue LED, 930 is a buffer layer fora blue LED, 928 is a blue multiple quantum well, 927 is a N-typeconfinement layer for a blue LED, 948 and 922 are ITO layers, 921 is anoptional reflector, 920 is a P-type confinement layer for a green LED,918 is a buffer layer for a green LED, 916 is a multiple quantum wellfor a green LED, 915 is a N-type confinement layer for a green LED, 952and 910 are ITO layers, 909 is a reflector, 908 is a P-type confinementlayer for a red LED, 906 is a red multiple quantum well, 905 is a N-typeconfinement layer for a red LED, 956 is an ITO layer, 958 is areflecting layer such as aluminum or silver, 962 is a metal viaconstructed, for example, out of aluminum, 960 is an air-gap or an oxidelayer, 964 is a nickel layer, and 966 is a solder bump.

FIG. 10 illustrates an embodiment of this invention, where stacked RGBLEDs are formed with control and driver circuits as well as imagesensors for the LED built on the silicon sub-mount 1068. Image sensorsessentially monitor the light coming out of the LED and tune the voltageand current given by control and driver circuits such that light outputof the LED is the right color and intensity. 1046 is a glass substrate,1044 and 1034 are ITO layers, 1033 is an optional reflector, 1032 is aP-type confinement layer for a blue LED, 1030 is a buffer layer for ablue LED, 1028 is a blue multiple quantum well, 1027 is a N-typeconfinement layer for a blue LED, 1048 and 1022 are ITO layers, 1021 isan optional reflector, 1020 is a P-type confinement layer for a greenLED, 1018 is a buffer layer for a green LED, 1016 is a multiple quantumwell for a green LED, 1015 is a N-type confinement layer for a greenLED, 1052 and 1010 are ITO layers, 1009 is a reflector, 1008 is a P-typeconfinement layer for a red LED, 1006 is a red multiple quantum well,1005 is a N-type confinement layer for a red LED, 1056 is an ITO layer,1058 is a reflecting layer such as aluminum or silver, 1062 is a metalvia constructed for example out of aluminum, 1060 is an air-gap or anoxide layer, 1064 is a nickel layer and 1066 is a solder bump. The viahole 1074 helps transfer light produced by the blue multiple quantumwell 1028 reach an image sensor on the silicon sub-mount 1068. The viahole 1072 helps transfer light produced by the green multiple quantumwell 1016 to an image sensor on the silicon sub-mount 1068. The via hole1070 helps transfer light produced by the red multiple quantum well 1006reach an image sensor on the silicon sub-mount 1068. By sampling thelight produced by each of the quantum wells on the LED, voltage andcurrent drive levels to different terminals of the LED can bedetermined. Color tunability, temperature compensation, better colorstability, and many other features can be obtained with this scheme.Furthermore, circuits to communicate wirelessly with the LED can beconstructed on the silicon sub-mount. Light output of the LED can bemodulated by a signal from the user delivered wirelessly to the light.

While three LED layers, namely, red, green, and blue, are shown asstacked in various embodiments of this invention, it will be clear toone skilled in the art based on the present disclosure that more thanthree LED layers can also be stacked. For example, red, green, blue andyellow LED layers can be stacked.

The embodiments of this invention described in FIGS. 4-FIG. 10 share afew common features. They have multiple stacked (or overlying) layers,they are constructed using smart layer transfer techniques and at leastone of the stacked layers has a thickness less than 50 microns. Whencleave is done using ion-cut, substrate layers that are removed usingcleave can be reused after a process flow that often includes a CMP.

FIGS. 11A-F show a prior art illustration of phosphor-coated LEDs(pcLEDs) constructed with ion-cut processes. The process begins in FIG.11A with a bulk-GaN substrate 1102, and an oxide layer 1104 is depositedatop it. The oxide layer 1104 is an oxide compatible with GaN. FIG. 11Bdepicts hydrogen being implanted into the structure shown in FIG. 11A ata certain depth (for ion-cut purposes). 1102 and 1104 have beendescribed previously with respect to FIG. 11A. Dotted lines 1106indicate the plane of hydrogen ions. Alternatively, helium can beimplanted instead of hydrogen or hydrogen and helium can beco-implanted. FIG. 11C shows a silicon wafer 1108 with an oxide layer1110 atop it. The structure shown in FIG. 11B is flipped and bonded atopthe structure shown in FIG. 11C using oxide-to-oxide bonding of layers1104 and 1110. This is depicted in FIG. 11D. 1108, 1110 and 1106 havebeen described previously. FIG. 11E shows the next step in the process.Using an anneal, a cleave is conducted at the plane of hydrogen atoms1106 shown in FIG. 11D, and a CMP is done to form GaN layer 1112. 1104,1110 and 1108 have been described previously. FIG. 11F shows thefollowing step in the process. A blue LED 1114 is grown epitaxiallyabove the GaN layer 1112. 1104, 1108 and 1110 have been describedpreviously. A phosphor layer can be coated atop the blue LED 1114 toform a white phosphor coated LED.

There may be some severe challenges with the prior art process shown inFIGS. 11A-F. The thermal expansion coefficients for GaN layers 1112 inFIG. 11F are very different from that for silicon layers 1108. Thisdifference can cause cracks and defects while growing the blue LED layer1114 at high temperatures (>600° C.), which usually occurs. These cracksand defects, in turn, cause bad efficiency and can in turn cause thephosphor coated LED process in FIG. 11A-F to be difficult tomanufacture. Furthermore, an anneal (typically >400° C.) is typicallyused in FIG. 11E to cleave the bulk GaN layers. This can again causeissues with mismatch of thermal expansion coefficients and causecracking and defects.

FIGS. 12A-F describe an embodiment of this invention, where phosphorcoated LEDs are formed with an ion-cut process (i.e. a smart layertransfer process). It minimizes the problem with mismatch of thermalexpansion co-efficients that is inherent to the process described inFIGS. 11A-F. This process could include several steps as described inthe following sequence:

Step (A): FIG. 12A illustrates this step. A blue LED wafer isconstructed on a bulk-GaN substrate 1216. For discussions within thisdocument, the bulk-GaN substrate could be semi-polar or non-polar orpolar. The blue LED wafer includes a N-type confinement layer 1214, amultiple quantum well (MQW) 1212, a buffer layer 1210, a P-typeconfinement layer 1208, an optional reflector 1204 and an ITO currentspreader 1206. Examples of materials used to construct these blue LEDlayers, include, but are not limited to, doped GaN for the N-type andP-type confinement layers 1214 and 1208, AlGaN for the buffer layer 1210and InGaN/GaN for the multiple quantum wells 1212. The optionalreflector 1204 could be distributed Bragg Reflector, an Aluminum orsilver layer or some other type of reflectors. A silicon dioxide layer1202 is deposited atop the optional reflector 1204.Step (B): FIG. 12B illustrates this step. The blue LED wafer describedin FIG. 12A has hydrogen implanted into it at a certain depth. Thedotted lines 1218 depict the hydrogen implant. Alternatively, helium canbe implanted. Various elements in FIG. 12B such as 1216, 1214, 1212,1210, 1208, 1206, 1204, and 1202 have been described previously.Step (C): FIG. 12C illustrates this step. A silicon wafer 1220 havingthe same wafer size as the structure in FIG. 12B is taken and an oxidelayer 1222 is grown or deposited atop it.Step (D): FIG. 12D illustrates this step. The structure shown in FIG.12B is flipped and bonded atop the structure shown in FIG. 12C usingoxide-to-oxide bonding of layers 1202 and 1222. Various elements in FIG.12D such as 1216, 1214, 1212, 1210, 1208, 1206, 1204, 1220, 1222, 1218and 1202 have been described previously.Step (E): FIG. 12E illustrates this step. The structure shown in FIG.12D is cleaved at its hydrogen plane 1218. A mechanical cleave may bepreferably used for this process, although an anneal could be used aswell. The mechanical cleave process typically happens at roomtemperatures, and therefore can avoid issues with thermal expansioncoefficients mismatch. After cleave, the wafer is planarized and theN-type confinement layer 1215 is formed. Various elements in FIG. 12Esuch as 1212, 1210, 1208, 1206, 1204, 1220, 1222, and 1202 have beendescribed previously. The bulk GaN substrate 1216 from FIG. 12D that hasbeen cleaved away can be reused. This may be attractive from a costperspective, since bulk GaN substrates are quite costly.Step (F): This is illustrated in FIG. 12F. An ITO layer 1224 isdeposited atop the structure shown in FIG. 12E. Various elements in FIG.12F such as 1212, 1210, 1208, 1206, 1204, 1220, 1222, 1215, 1224, and1202 have been described previously.The advantage of the process shown in FIG. 12A-F over the process shownin FIG. 11A-F may include low process temperatures, even less than 250°C. Therefore, issues with thermal expansion co-efficients mismatch aresubstantially mitigated. While the description in FIG. 12A-F is for aLED, many other devices, such as, for example, laser diodes, high powertransistors, high frequencies transistors, special transmitter circuitsand many other devices can be constructed, according to a similardescription, with bulk-GaN.

NuImager Technology:

Layer transfer technology can also be advantageously utilized forconstructing image sensors. Image sensors typically includephotodetectors on each pixel to convert light energy to electricalsignals. These electrical signals are sensed, amplified and stored asdigital signals using transistor circuits.

FIG. 13 shows prior art where through-silicon via (TSV) technology isutilized to connect photodetectors 1302 on one layer (tier) of siliconto transistor read-out circuits 1304 on another layer (tier) of silicon.Unfortunately, pixel sizes in today's image sensors are 1.1 μm or so. Itis difficult to get through-silicon vias with size <1 μm due toalignment problems, leading to a diminished ability to utilizethrough-silicon via technology for future image sensors. In FIG. 13,essentially, transistors can be made for read-out circuits in one wafer,photodetectors can be made on another wafer, and then these wafers canbe bonded together with connections made with through-silicon vias.

FIGS. 14-21 describe some embodiments of this invention, wherephotodetector and read-out circuits are stacked monolithically withlayer transfer. FIG. 14 shows two configurations for stackingphotodetectors and read-out circuits. In one configuration, denoted as1402, a photodetector layer 1406 is formed above read-out circuit layer1408 with connections 1404 between these two layers. In anotherconfiguration, denoted as 1410, photodetectors 1412 may have read-outcircuits 1414 formed above them, with connecting 1416 between these twolayers.

FIGS. 15A-H describe an embodiment of this invention, where an imagesensor includes a photodetector layer formed atop a read-out circuitlayer using layer transfer. In this document, the photodetector layer isdenoted as a p-n junction layer. However, any type of photodetectorlayer, such as a pin layer or some other type of photodetector can beused. The thickness of the photodetector layer is typically less than 5μm. The process of forming the image sensor could include several stepsthat occur in a sequence from Step (A) to Step (H). Many of these stepsshare common characteristics, features, modes of operation, etc. Whenidentical reference numbers are used in different drawing figures, theyare used to indicate analogous, similar or identical structures toenhance the understanding of the present invention by clarifying therelationships between the structures and embodiments presented in thevarious diagrams—particularly in relating analogous, similar oridentical functionality to different physical structures.

Step (A) is illustrated in FIG. 15A. A silicon wafer 1502 is taken and an+ Silicon layer 1504 is ion implanted. Following this, n layer 1506, player 1508 and p+ layer 1510 are formed epitaxially. It will beappreciated by one skilled in the art based on the present disclosurethat there are various other procedures to form the structure shown inFIG. 15A. An anneal is then performed to activate dopants in variouslayers.Step (B) is illustrated in FIG. 15B. Various elements in FIG. 15B suchas 1502, 1504, 1506, 1508 and 1510 have been described previously. Usinglithography and etch, a via is etched into the structure shown in FIG.15A, filled with oxide and polished with CMP. The regions formed afterthis process are the oxide filled via 1512 and the oxide layer 1514. Theoxide filled via 1512 may also be referred to as an oxide via or anoxide window region or oxide aperture. A cross-section of the structureis indicated by 1598 and a top view is indicated by 1596. 1516 indicatesalignment marks and the oxide filled via 1512 is formed in place of someof the alignment marks printed on the wafer.Step (C) is illustrated in FIG. 15C. Various elements in FIG. 15C suchas 1502, 1504, 1506, 1508, 1510, 1512, 1514, and 1516 have beendescribed previously. Hydrogen is implanted into the structure indicatedin FIG. 15B at a certain depth indicated by dotted lines 1518 of FIG.15C. Alternatively, Helium can be used as the implanted species. Across-sectional view 1594 and a top view 1592 are shown.Step (D) is illustrated in FIG. 15D. A silicon wafer 1520 with read-outcircuits (which includes wiring) processed on it is taken, and an oxidelayer 1522 is deposited above it.Step (E) is illustrated in FIG. 15E. The structure shown in FIG. 15C isflipped and bonded to the structure shown in FIG. 15D usingoxide-to-oxide bonding of oxide layers 1514 and 1522. During thisbonding procedure, alignment is done such that oxide vias 1512 (shown inthe top view 1526 of the photodetector wafer) are above alignment marks(such as 1530) on the top view 1528 of the read-out circuit wafer. Across-sectional view of the structure is shown with 1524. Variouselements in FIG. 15E such as 1502, 1504, 1506, 1508, 1510, 1512, 1514,1516, 1518, 1520, and 1522 have been described previously.Step (F) is illustrated in FIG. 15F. The structure shown in FIG. 15E maybe cleaved at its hydrogen plane 1518 preferably using a mechanicalprocess. Alternatively, an anneal could be used for this purpose. A CMPprocess may be then done to planarize the surface resulting in a finaln+ silicon layer indicated as 1534. 1525 depicts a cross-sectional viewof the structure after the cleave and CMP process. Various elements inFIG. 15F such as 1506, 1508, 1510, 1512, 1514, 1516, 1518, 1520, 1526,1524, 1530, 1528, 1532 and 1522 have been described previously.Step (G) is illustrated using FIG. 15G. Various elements in FIG. 15Gsuch as 1506, 1508, 1510, 1512, 1514, 1516, 1518, 1520, 1526, 1524,1530, 1528, 1532, 1534 and 1522 have been described previously. An oxidelayer 1540 is deposited. Connections between the photodetector andread-out circuit wafers are formed with metal 1538 and an insulatorcovering 1536. These connections are formed well aligned to the read-outcircuit layer 1520 by aligning to alignment marks 1530 on the read-outcircuit layer 1520 through oxide vias 1512. 1527 depicts across-sectional view of the structure.Step (H) is illustrated in FIG. 15H. Connections are made to theterminals of the photodetector and are indicated as 1542 and 1544.Various elements of FIG. 15H such as 1520, 1522, 1512, 1514, 1510, 1508,1506, 1534, 1536, 1538, 1540, 1542, and 1544 have been describedpreviously. Contacts and interconnects for connecting terminals of thephotodetector to read-out circuits are then done, following which apackaging process is conducted.

FIGS. 15A-G show a process where oxide vias may be used to look throughphotodetector layers to observe alignment marks on the read-out circuitwafer below it. However, if the thickness of the silicon on thephotodetector layer is <100-400 nm, the silicon wafer is thin enoughthat one can look through it without requiring oxide vias. A processsimilar to FIG. 15A-G where the silicon thickness for the photodetectoris <100-400 nm represents another embodiment of this invention. In thatembodiment, oxide vias may not be constructed and one could look rightthrough the photodetector layer to observe alignment marks of theread-out circuit layer. This may help making well-alignedthrough-silicon connections between various layers.

As mentioned previously, FIGS. 15A-G illustrate a process where oxidevias constructed before layer transfer are used to look throughphotodetector layers to observe alignment marks on the read-out circuitwafer below it. However, an alternative embodiment of this invention mayinvolve constructing oxide vias after layer transfer. Essentially, afterlayer transfer of structures without oxide vias, oxide vias whosediameters are larger than the maximum misalignment of thebonding/alignment scheme are formed. This order of sequences may enableobservation of alignment marks on the bottom read-out circuit wafer bylooking through the photodetector wafer.

While Silicon has been suggested as the material for the photodetectorlayer of FIG. 15A-G, Germanium could be used in an alternativeembodiment. The advantage of Germanium is that it is sensitive toinfra-red wavelengths as well. However, Germanium also suffers from highdark current.

While FIG. 15A-G described a single p-n junction as the photodetector,it will be obvious to one skilled in the art based on the presentdisclosure that multiple p-n junctions can be formed one on top of eachother, as described in “Color Separation in an Active Pixel Cell ImagingArray Using a Triple-Well Structure,” U.S. Pat. No. 5,965,875, 1999 byR. Merrill and in “Trends in CMOS Image Sensor Technology and Design,”International Electron Devices Meeting Digest of Technical Papers, 2002by A. El-Gamal. This concept relies on the fact that differentwavelengths of light penetrate to different thicknesses of silicon, asdescribed in FIG. 16. It can be observed in FIG. 16 that near thesurface 400 nm wavelength light has much higher absorption per unitdepth than 450 nm-650 nm wavelength light. On the other hand, at a depthof 0.5 μm, 500 nm light has a higher absorption per unit depth than 400nm light. An advantage of this approach is that one does not requireseparate filters (and area) for green, red and blue light; all thesedifferent colors/wavelengths of light can be detected with different p-njunctions stacked atop each other. So, the net area required fordetecting three different colors of light is reduced, leading to animprovement of resolution.

FIGS. 17A-B illustrate an embodiment of this invention, where red,green, and blue photodetectors are stacked monolithically atop read-outcircuits using ion-cut technology (for an image sensor). Therefore, asmart layer transfer technique is utilized. FIG. 17A shows the firststep for constructing this image sensor. 1724 shows a cross-sectionalview of 1708, a silicon wafer with read-out circuits constructed on it,above which an oxide layer 1710 is deposited. 1726 shows thecross-sectional view of another wafer which has a p+ Silicon layer 1714,a p Silicon layer 1716, a n Silicon layer 1718, a n+ Silicon layer 1720,and an oxide layer 1722. These layers are formed using proceduressimilar to those described in FIG. 15A-G. An anneal is then performed toactivate dopants in various layers. Hydrogen is implanted in the waferat a certain depth depicted by 1798. FIG. 17B shows the structure of theimage sensor before contact formation. Three layers of p+pnn+ silicon(each corresponding to a color band and similar to the one depicted in1726 in FIG. 17A) are layer transferred sequentially atop the siliconwafer with read-out circuits (depicted by 1724 in FIG. 17A). Threedifferent layer transfer steps may be used for this purpose. Proceduresfor layer transfer and alignment for forming the image sensor in FIG.17B are similar to procedures used for constructing the image sensorshown in FIGS. 15A-G. Each of the three layers of p+pnn+ silicon sensesa different wavelength of light. For example, blue light is detected byblue photodetector 1702, green light is detected by green photodetector1704, and red light is detected by red photodetector 1706. Contacts,metallization, packaging and other steps are done to the structure shownin FIG. 17B to form an image sensor. The oxides 1730 and 1732 could beeither transparent conducting oxides or silicon dioxide. Use oftransparent conducting oxides could allow fewer contacts to be formed.

FIG. 18A-B show another embodiment of this invention, where red, greenand blue photodetectors are stacked monolithically atop read-outcircuits using ion-cut technology (for an image sensor) using adifferent configuration. Therefore, a smart layer transfer technique isutilized. FIG. 18A shows the first step for constructing this imagesensor. 1824 shows a cross-section of 1808, a silicon wafer withread-out circuits constructed on it, above which an oxide layer 1810 isdeposited. 1826 shows the cross-sectional view of another wafer whichhas a p+ Silicon layer 1814, a p Silicon layer 1816, a n Silicon layer1818, a p Silicon layer 1820, a n Silicon layer 1822, a n+ Silicon layer1828 and an oxide layer 1830. These layers may be formed usingprocedures similar to those described in FIG. 15A-G. An anneal is thenperformed to activate dopants in various layers. Hydrogen is implantedin the wafer at a certain depth depicted by 1898. FIG. 18B shows thestructure of the image sensor before contact formation. A layer ofp+pnpnn+ (similar to the one depicted in 1826 in FIG. 18A) is layertransferred sequentially atop the silicon wafer with read-out circuits(depicted by 1824 in FIG. 18A). Procedures for layer transfer andalignment for forming the image sensor in FIG. 18B are similar toprocedures used for constructing the image sensor shown in FIG. 15A-G.Contacts, metallization, packaging and other steps are done to thestructure shown in FIG. 18B to form an image sensor. Three different pnjunctions, denoted by 1802, 1804 and 1806 may be formed in the imagesensor to detect different wavelengths of light.

FIGS. 19A-B show another embodiment of this invention, where an imagesensor that can detect both visible and infra-red light is depicted.Such image sensors could be useful for taking photographs in both dayand night settings (without necessarily requiring a flash). Thisembodiment makes use of the fact that while silicon is not sensitive toinfra-red light, other materials such as Germanium and Indium GalliumArsenide are. A smart layer transfer technique is utilized for thisembodiment. FIG. 19A shows the first step for constructing this imagesensor. 1902 shows a cross-sectional view of 1904, a silicon wafer withread-out circuits constructed on it, above which an oxide layer 1906 isdeposited. 1908 shows the cross-sectional view of another wafer whichhas a p+ Silicon layer 1912, a p Silicon layer 1914, a n Silicon layer1916, a n+ Silicon layer 1918 and an oxide layer 1720. These layers maybe formed using procedures similar to those described in FIGS. 15A-G. Ananneal is then performed to activate dopants in various layers. Hydrogenis implanted in the wafer at a certain depth depicted by 1998. 1922shows the cross-sectional view of another wafer which has a substrate1924, an optional buffer layer 1936, a p+ Germanium layer 1926, a pGermanium layer 1924, a n Germanium layer 1922, a n+ Germanium layer1920 and an oxide layer 1934. These layers are formed using proceduressimilar to those described in FIGS. 15A-G. An anneal is then performedto activate dopants in various layers. Hydrogen is implanted in thewafer at a certain depth depicted by 1996. Examples of materials usedfor the structure 1922 include a Germanium substrate for 1924, no bufferlayer and multiple Germanium layers. Alternatively, a Indium Phosphidesubstrate could be used for 1924 when the layers 1926, 1924, 1922 and1920 are constructed of InGaAs instead of Germanium. FIG. 19B shows thestructure of this embodiment of the invention before contacts andmetallization are constructed. The p+pnn+ Germanium layers of structure1922 of FIG. 19A are layer transferred atop the read-out circuit layerof structure 1902. This is done using smart layer transfer proceduressimilar to those described in respect to FIG. 15A-G. Following this,multiple p+pnn+ layers similar to those used in structure 1908 are layertransferred atop the read-out circuit layer and Germanium photodetectorlayer (using three different layer transfer steps). This, again, is doneusing procedures similar to those described in FIGS. 15A-G. Thestructure shown in FIG. 19B therefore has a layer of read-out circuits1904, above which an infra-red photodetector 1944, a red photodetector1942, a green photodetector 1940 and a blue photodetector 1938 arepresent. Procedures for layer transfer and alignment for forming theimage sensor in FIG. 19B are similar to procedures used for constructingthe image sensor shown in FIG. 15A-G. Each of the p+pnn+ layers senses adifferent wavelength of light. Contacts, metallization, packaging andother steps are done to the structure shown in FIG. 19B to form an imagesensor. The oxides 1946, 1948, and 1950 could be either transparentconducting oxides or silicon dioxide. Use of transparent conductingoxides could allow fewer contacts to be formed.

FIG. 20A describes another embodiment of this invention, wherepolarization of incoming light can be detected. The p-n junctionphotodetector 2006 detects light that has passed through a wire gridpolarizer 2004. Details of wire grid polarizers are described in“Fabrication of a 50 nm half-pitch wire grid polarizer using nanoimprintlithography.” Nanotechnology 16 (9): 1874-1877, 2005 by Ahn, S. W.; K.D. Lee, J. S. Kim, S. H. Kim, J. D. Park, S. H. Lee, P. W. Yoon. Thewire grid polarizer 2004 absorbs one plane of polarization of theincident light, and may enable detection of other planes of polarizationby the p-n junction photodetector 2006. The p-n junction photodetector2002 detects all planes of polarization for the incident light, while2006 detects the planes of polarization that are not absorbed by thewire grid polarizer 2004. One can thereby determine polarizationinformation from incoming light by combining results from photodetectors2002 and 2006. The device described in FIG. 20A can be fabricated byfirst constructing a silicon wafer with transistor circuits 2008,following which the p-n junction photodetector 2006 can be constructedwith the low-temperature layer transfer techniques described in FIG.15A-G. Following this construction of p-n junction photodetector 2006,the wire grid polarizer 2004 may be constructed using standardintegrated circuit metallization methods. The photodetector 2002 canthen be constructed by another low-temperature layer transfer process asdescribed in FIG. 15A-G. One skilled in the art, based on the presentdisclosure, can appreciate that low-temperature layer transfertechniques are critical to build this device, since semiconductor layersin 2002 are built atop metallization layers required for the wire gridpolarizer 2004. Thickness of the photodetector layers 2002 and 2006 maybe preferably less than 5 μm. An example with polarization detectionwhere the photodetector has other pre-processed optical interactionlayers (such as a wire grid polarizer) has been described herein.However, other devices for determining parameters of incoming light(such as phase) may be constructed with layer transfer techniques.

One of the common issues with taking photographs with image sensors isthat in scenes with both bright and dark areas, while the exposureduration or shutter time could be set high enough to get enough photonsin the dark areas to reduce noise, picture quality in bright areasdegrades due to saturation of the photodetectors' characteristics. Thisissue is with the dynamic range of the image sensor, i.e. there is atradeoff between picture quality in dark and bright areas. FIG. 20Bshows an embodiment of this invention, where higher dynamic range can bereached. According the embodiment of FIG. 20B, two layers ofphotodetectors 2032 and 2040, could be stacked atop a read-out circuitlayer 2028. 2026 is a schematic of the architecture. Connections 2030run between the photodetector layers 2032 and 2040 and the read-outcircuit layer 2028. 2024 are reflective metal lines that block lightfrom reaching part of the bottom photodetector layer 2032. 2042 is a topview of the photodetector layer 2040. Photodetectors 2036 could bepresent, with isolation regions 2038 between them. 2044 is a top view ofthe photodetector layer 2032 and the metal lines 2024. Photodetectors2048 are present, with isolation regions 2046 between them. A portion ofthe photodetectors 2048 can be seen to be blocked by metal lines 2024.Brighter portions of an image can be captured with photodetectors 2048,while darker portions of an image can be captured with photodetectors2036. The metal lines 2024 positioned in the stack may substantiallyreduce the number of photons (from brighter portions of the image)reaching the bottom photodetectors 2048. This reduction in number ofphotons reaching the bottom photodetectors 2048 helps keep the dynamicrange high. Read-out signals coming from both dark and bright portionsof the photodetectors could be used to get the final picture from theimage sensor.

FIG. 21 illustrates another embodiment of this invention where aread-out circuit layer 2104 is monolithically stacked above thephotodetector layer 2102 at a temperature approximately less than 400°C. Connections 2106 are formed between these two layers. Procedures forstacking high-quality monocrystalline transistor circuits and wires attemperatures approximately less than 400° C. using layer transfer aredescribed in pending U.S. patent application Ser. No. 12/901,890 byauthors of this patent application. The stacked layers could usejunction-less transistors, recessed channel transistors, repeatinglayouts or other devices/techniques described U.S. patent applicationSer. No. 12/901,890.

The embodiments of this invention described in FIG. 14-FIG. 21 may sharea few common features. They can have multiple stacked (or overlying)layers, use one or more photodetector layers (terms photodetector layersand image sensor layers are often used interchangeably), thickness of atleast one of the stacked layers is less than 5 microns and constructioncan be done with smart layer transfer techniques and are stacking isdone at temperatures approximately less than 450° C.

NuDisplay Technology:

In displays and microdisplays (small size displays where opticalmagnification is needed), transistors need to be formed on glass orplastic substrates. These substrates typically cannot withstand highprocess temperatures (e.g., >400° C.). Layer transfer can beadvantageously used for constructing displays and microdisplays as well,since it may enable transistors to be processed on these substrates at<400° C. Various embodiments of transistors constructed on glasssubstrates are described in this patent application. These transistorsconstructed on glass substrates could form part of liquid crystaldisplays (LCDs) or other types of displays. It will be clear to thoseskilled in the art based on the present disclosure that these techniquescan also be applied to plastic substrates.

FIGS. 22A-G describe a process for forming recessed channel singlecrystal (or monocrystalline) transistors on glass substrates at atemperature approximately less than 400° C. for display and microdisplayapplications. This process could include several steps that occur in asequence from Step (A) to Step (G). Many of these steps share commoncharacteristics, features, modes of operation, etc. When identicalreference numbers are used in different drawing figures, they are usedto indicate analogous, similar or identical structures to enhance theunderstanding of the present invention by clarifying the relationshipsbetween the structures and embodiments presented in the variousdiagrams—particularly in relating analogous, similar or identicalfunctionality to different physical structures.

Step (A) is illustrated in FIG. 22A. A silicon wafer 2202 is taken and an+ region 2204 is formed by ion implantation. Following this formation,a layer of p− Silicon 2206 is epitaxially grown. An oxide layer 2210 isthen deposited. Following this deposition, an anneal is performed toactivate dopants in various layers. It will be clear to one skilled inthe art based on the present disclosure that various other procedurescan be used to get the structure shown in FIG. 22A.Step (B) is illustrated in FIG. 22B. Hydrogen is implanted into thestructure shown in FIG. 22A at a certain depth indicated by 2212.Alternatively, Helium can be used for this purpose. Various elements inFIG. 22B, such as 2202, 2204, 2006, and 2210 have been describedpreviously.Step (C) is illustrated in FIG. 22C. A glass substrate 2214 is taken anda silicon oxide layer 2216 is deposited atop it at compatibletemperatures.Step (D) is illustrated in FIG. 22D. Various elements in FIG. 22D, suchas 2202, 2204, 2206, 2210, 2214, and 2216 have been describedpreviously. The structure shown in FIG. 22B is flipped and bonded to thestructure shown in FIG. 22C using oxide-to-oxide bonding of layers 2210and 2216.Step (E) is illustrated in FIG. 22E. The structure shown in FIG. 22D iscleaved at the hydrogen plane 2212 of FIG. 22D. A CMP is then done toplanarize the surface and yield the n+ Si layer 2218. Various otherelements in FIG. 22E, such as 2214, 2216, 2210 and 2206 have beendescribed previously.Step (F) is illustrated in FIG. 22F. Various elements in FIG. 22F suchas 2214, 2216, 2210, and 2206 have been described previously. An oxidelayer 2220 is formed using a shallow trench isolation (STI) process.This helps isolate transistors.Step (G) is illustrated in FIG. 22G. Various elements in FIG. 22G suchas 2210, 2216, 2220 and 2214 have been described previously. Using etchtechniques, part of the n+ Silicon layer from FIG. 22F and optionally p−Silicon layer from FIG. 22F are etched. After this a thin gatedielectric is deposited, after which a gate dielectrode is deposited.The gate dielectric and gate electrode are then polished away to formthe gate dielectric layer 2224 and gate electrode layer 2222. The n+Silicon layers 2228 and 2226 form the source and drain regions of thetransistors while the p− Silicon region after this step is indicated by2230. Contacts and other parts of the display/microdisplay are thenfabricated. It can be observed that during the whole process, the glasssubstrate substantially always experiences temperatures less than 400°C., or even lower. This is because the crystalline silicon can betransferred atop the glass substrate at a temperature less than 400° C.,and dopants are pre-activated before layer transfer to glass.

FIG. 23A-H describes a process of forming both nMOS and pMOS transistorswith single-crystal silicon on a glass substrate at temperatures lessthan 400° C., and even lower. Ion-cut technology (which is a smart layertransfer technology) is used. While the process flow described is shownfor both nMOS and pMOS on a glass substrate, it could also be used forjust constructing nMOS devices or for just constructing pMOS devices.This process could include several steps that occur in a sequence fromStep (A) to Step (H). Many of these steps share common characteristics,features, modes of operation, etc. When identical reference numbers areused in different drawing figures, they are used to indicate analogous,similar or identical structures to enhance the understanding of thepresent invention by clarifying the relationships between the structuresand embodiments presented in the various diagrams—particularly inrelating analogous, similar or identical functionality to differentphysical structures.

Step (A) is illustrated in FIG. 23A. A p− Silicon wafer 2302 is takenand a n well 2304 is formed on the p− Silicon wafer 2302. Variousadditional implants to optimize dopant profiles can also be done.Following this formation, an isolation process is conducted to formisolation regions 2306. A dummy gate dielectric 2310 made of silicondioxide and a dummy gate electrode 2308 made of polysilicon areconstructed.Step (B) is illustrated in FIG. 23B. Various elements of FIG. 23B, suchas 2302, 2304, 2306, 2308 and 2310 have been described previously.Implants are done to form source-drain regions 2312 and 2314 for bothnMOS and pMOS transistors. A rapid thermal anneal (RTA) is then done toactivate dopants. Alternatively, a spike anneal or a laser anneal couldbe done.Step (C) is illustrated in FIG. 23C. Various elements of FIG. 23C suchas 2302, 2304, 2306, 2308, 2310, 2312 and 2314 have been describedpreviously. An oxide layer 2316 is deposited and planarized with CMP.Step (D) is described in FIG. 23D. Various elements of FIG. 23D such as2302, 2304, 2306, 2308, 2310, 2312, 2314, and 2316 have been describedpreviously. Hydrogen is implanted into the wafer at a certain depthindicated by 2318. Alternatively, helium can be implanted.Step (E) is illustrated in FIG. 23E. Various elements of FIG. 23E suchas 2302, 2304, 2306, 2308, 2310, 2312, 2314, 2316, and 2318 have beendescribed previously. Using a temporary bonding adhesive, the oxidelayer is bonded to a temporary carrier wafer 2320. An example of atemporary bonding adhesive is a polyimide that can be removed by shininga laser. An example of a temporary carrier wafer is glass.Step (F) is described in FIG. 23F. The structure shown in FIG. 23E iscleaved at the hydrogen plane using a mechanical force. Alternatively,an anneal could be used. Following this cleave, a CMP is done toplanarize the surface. An oxide layer is then deposited. FIG. 23F showsthe structure after all these steps are done, with the deposited oxidelayer indicated as 2328. After the cleave, the p− Silicon region isindicated as 2322, the n− Silicon region is indicated as 2324, and theoxide isolation regions are indicated as 2326. Various other elements inFIG. 23F such as 2308, 2320, 2312, 2314, 2310, and 2316 have beendescribed previously.Step (G) is described in FIG. 23G. The structure shown in FIG. 23F isbonded to a glass substrate 2332 with an oxide layer 2330 usingoxide-to-oxide bonding. Various elements in FIG. 23G such as 2308, 2326,2322, 2324, 2312, 2314, and 2310 have been described previously. Oxideregions 2328 and 2330 are bonded together. The temporary carrier waferfrom FIG. 23F is removed by shining a laser through it. A CMP process isthen conducted to reach the surface of the gate electrode 2308. Theoxide layer remaining is denoted as 2334.Step (H) is described in FIG. 23H. Various elements in FIG. 23H such as2312, 2314, 2328, 2330, 2332, 2334, 2326, 2324, and 2322 have beendescribed previously. The dummy gate dielectric and dummy gate electrodeare etched away in this step and a replacement gate dielectric 2336 anda replacement gate electrode 2338 are deposited and planarized with CMP.Examples of replacement gate dielectrics could be hafnium oxide oraluminum oxide while examples of replacement gate electrodes could beTiN or TaN or some other material. Contact formation, metallization andother steps for building a display/microdisplay are then conducted. Itcan be observed that after attachment to the glass substrate, no processstep requires a processing temperature above 400° C.

FIGS. 24A-F describe an embodiment of this invention, wheresingle-crystal Silicon junction-less transistors are constructed aboveglass substrates at a temperature approximately less than 400° C. Anion-cut process (which is a smart layer transfer process) is utilizedfor this purpose. This process could include several steps that occur ina sequence from Step (A) to Step (F). Many of these steps share commoncharacteristics, features, modes of operation, etc. When identicalreference numbers are used in different drawing figures, they are usedto indicate analogous, similar or identical structures to enhance theunderstanding of the present invention by clarifying the relationshipsbetween the structures and embodiments presented in the variousdiagrams—particularly in relating analogous, similar or identicalfunctionality to different physical structures.

Step (A) is illustrated in FIG. 24A. A glass substrate 2402 is taken anda layer of silicon oxide 2404 is deposited on the glass substrate 2402.Step (B) is illustrated in FIG. 24B. A p− Silicon wafer 2406 isimplanted with a n+ Silicon layer 2408 above which an oxide layer 2410is deposited. A RTA or spike anneal or laser anneal is conducted toactivate dopants. Following this, hydrogen is implanted into the waferat a certain depth indicated by 2412. Alternatively, helium can beimplanted.Step (C) is illustrated in FIG. 24C. The structure shown in FIG. 24B isflipped and bonded onto the structure shown in FIG. 24A usingoxide-to-oxide bonding. This bonded structure is cleaved at its hydrogenplane, after which a CMP is done. FIG. 24C shows the structure after allthese processes are completed. 2414 indicates the n+ Si layer, while2402, 2404, and 2410 have been described previously.Step (D) is illustrated in FIG. 24D. A lithography and etch process isconducted to pattern the n+ Silicon layer 2414 in FIG. 24C to form n+Silicon regions 2418 in FIG. 24D. The glass substrate is indicated as2402 and the bonded oxide layers 2404 and 2410 are shown as well.Step (E) is illustrated in FIG. 24E. A gate dielectric 2420 and gateelectrode 2422 are deposited, following which a CMP is done. 2402 is asdescribed previously. The n+ Si regions 2418 are not visible in thisfigure, since they are covered by the gate electrode 2422. Oxide regions2404 and 2410 have been described previously.Step (F) is illustrated in FIG. 24F. The gate dielectric 2420 and gateelectrode 2422 from FIG. 24E are patterned and etched to form thestructure shown in FIG. 24F. The gate dielectric after the etch processis indicated as 2424 while the gate electrode after the etch process isindicated as 2426. n+ Si regions are indicated as 2418 while the glasssubstrate is indicated as 2402. Oxide regions 2404 and 2410 have beendescribed previously. It can be observed that a three-side gatedjunction-less transistor is formed at the end of the process describedwith respect of FIGS. 24A-F. Contacts, metallization and other steps forconstructing a display/microdisplay are performed after the stepsindicated by FIGS. 24A-F. It can be seen that the glass substrate is notexposed to temperatures greater than approximately 400° C. during anystep of the above process for forming the junction-less transistor.

FIGS. 25A-D describe an embodiment of this invention, where amorphous Sior polysilicon junction-less transistors are constructed above glasssubstrates at a temperature less than 400° C. This process could includeseveral steps that occur in a sequence from Step (A) to Step (D). Manyof these steps share common characteristics, features, modes ofoperation, etc. When identical reference numbers are used in differentdrawing figures, they are used to indicate analogous, similar oridentical structures to enhance the understanding of the presentinvention by clarifying the relationships between the structures andembodiments presented in the various diagrams—particularly in relatinganalogous, similar or identical functionality to different physicalstructures.

Step (A) is illustrated in FIG. 25A. A glass substrate 2502 is taken anda layer of silicon oxide 2504 is deposited on the glass substrate 2502.Following this deposition, a layer of n+ Si 2506 is deposited usinglow-pressure chemical vapor deposition (LPCVD) or plasma enhancedchemical vapor deposition (PECVD). This layer of n+ Si could optionallybe hydrogenated.Step (B) is illustrated in FIG. 25B. A lithography and etch process isconducted to pattern the n+ Silicon layer 2506 in FIG. 25A to form n+Silicon regions 2518 in FIG. 25B. 2502 and 2504 have been describedpreviously.Step (C) is illustrated in FIG. 25C. A gate dielectric 2520 and gateelectrode 2522 are deposited, following which a CMP is optionally done.2502 is as described previously. The n+ Si regions 2518 are not visiblein this figure, since they are covered by the gate electrode 2522.Step (D) is illustrated in FIG. 25D. The gate dielectric 2520 and gateelectrode 2522 from FIG. 25C are patterned and etched to form thestructure shown in FIG. 25D. The gate dielectric after the etch processis indicated as 2524 while the gate electrode after the etch process isindicated as 2526. n+ Si regions are indicated as 2518 while the glasssubstrate is indicated as 2502. It can be observed that a three-sidegated junction-less transistor is formed at the end of the processdescribed with respect of FIGS. 25A-D. Contacts, metallization and othersteps for constructing a display/microdisplay are performed after thesteps indicated by FIGS. 25A-D. It can be seen that the glass substrateis not exposed to temperatures greater than 400° C. during any step ofthe above process for forming the junction-less transistor.

FIGS. 26A-C illustrate an embodiment of this invention, where amicrodisplay is constructed using stacked RGB LEDs and control circuitsare connected to each pixel with solder bumps. This process couldinclude several steps that occur in a sequence from Step (A) to Step(C). Many of these steps share common characteristics, features, modesof operation, etc. When identical reference numbers are used indifferent drawing figures, they are used to indicate analogous, similaror identical structures to enhance the understanding of the presentinvention by clarifying the relationships between the structures andembodiments presented in the various diagrams—particularly in relatinganalogous, similar or identical functionality to different physicalstructures.

Step (A) is illustrated in FIG. 26A. Using procedures similar to FIG.4A-S, the structure shown in FIG. 26A is constructed. Various elementsof FIG. 26A are as follows:2646—a glass substrate,2644—an oxide layer, could be a conductive oxide such as ITO,2634—an oxide layer, could be a conductive oxide such as ITO2633—a an optional reflector, could be a Distributed Bragg Reflector orsome other type of reflector,2632—a P-type confinement layer that is used for a Blue LED (One exampleof a material for this region is GaN),2630—a buffer layer that is typically used for a Blue LED (One exampleof a material for this region is AlGaN),2628—a multiple quantum well used for a Blue LED (One example ofmaterials for this region are InGaN/GaN),2627—a N-type confinement layer that is used for a Blue LED (One exampleof a material for this region is GaN).2648—an oxide layer, may be preferably a conductive metal oxide such asITO,2622—an oxide layer, may be preferably a conductive metal oxide such asITO,2621—an optional reflector (for example, a Distributed Bragg Reflector),2620—a P-type confinement layer that is used for a Green LED (Oneexample of a material for this region is GaN),2618—a buffer layer that is typically used for a Green LED (One exampleof a material for this region is AlGaN),2616—a multiple quantum well used for a Green LED (One example ofmaterials for this region are InGaN/GaN),2615—a N-type confinement layer that is used for a Green LED (Oneexample of a material for this region is GaN),2652—an oxide layer, may be preferably a conductive metal oxide such asITO,2610—an oxide layer, may be preferably a conductive metal oxide such asITO,2609—an optional reflector (for example, a Distributed Bragg Reflector),2608—a P-type confinement layer used for a Red LED (One example of amaterial for this region is AlInGaP),2606—a multiple quantum well used for a Red LED (One example ofmaterials for this region are AlInGaP/GaInP),2604—a P-type confinement layer used for a Red LED (One example of amaterial for this region is AlInGaP),2656—an oxide layer, may be preferably a transparent conductive metaloxide such as ITO, and2658—a reflector (for example, aluminum or silver).Step (B) is illustrated in FIG. 26B. Via holes 2662 are etched to thesubstrate layer 2646 to isolate different pixels in themicrodisplay/display. Also, via holes 2660 are etched to make contactsto various layers of the stack. These via holes may be preferably notfilled. An alternative is to fill the via holes with a compatible oxideand planarize the surface with CMP. Various elements in FIG. 26B such as2646, 2644, 2634, 2633, 2632, 2630, 2628, 2627, 2648, 2622, 2621, 2620,2618, 2616, 2615, 2652, 2610, 2609, 2608, 2606, 2604, 2656 and 2658 havebeen described previously.Step (C) is illustrated in FIG. 26C. Using procedures similar to thosedescribed in respect to FIGS. 4A-S, the via holes 2660 have contacts2664 (for example, with Aluminum) made to them. Also, using proceduressimilar to those described in FIGS. 4A-S, nickel layers 2666, solderlayers 2668, and a silicon sub-mount 2670 with circuits integrated onthem are constructed. The silicon sub-mount 2670 has transistors tocontrol each pixel in the microdisplay/display. Various elements in FIG.26C such as 2646, 2644, 2634, 2633, 2632, 2630, 2628, 2627, 2648, 2622,2621, 2620, 2618, 2616, 2615, 2652, 2610, 2609, 2608, 2606, 2604, 2656,2660, 2662, and 2658 have been described previously.It can be seen that the structure shown in FIG. 26C can have each pixelemit a certain color of light by tuning the voltage given to the red,green and blue layers within each pixel. This microdisplay may beconstructed using the ion-cut technology, a smart layer transfertechnique.

FIGS. 27A-D illustrate an embodiment of this invention, where amicrodisplay is constructed using stacked RGB LEDs and control circuitsare integrated with the RGB LED stack. This process could includeseveral steps that occur in a sequence from Step (A) to Step (D). Manyof these steps share common characteristics, features, modes ofoperation, etc. When identical reference numbers are used in differentdrawing figures, they are used to indicate analogous, similar oridentical structures to enhance the understanding of the presentinvention by clarifying the relationships between the structures andembodiments presented in the various diagrams—particularly in relatinganalogous, similar or identical functionality to different physicalstructures.

Step (A) is illustrated in FIG. 27A. Using procedures similar to thoseillustrated in FIGS. 4A-S, the structure shown in FIG. 27A isconstructed. Various elements of FIG. 27A are as follows:2746—a glass substrate,2744—an oxide layer, could be a conductive oxide such as ITO,2734—an oxide layer, could be a conductive oxide such as ITO,2733—a an optional reflector (e.g., a Distributed Bragg Reflector orsome other type of reflector),2732—a P-type confinement layer that is used for a Blue LED (One exampleof a material for this region is GaN),2730—a buffer layer that is typically used for a Blue LED (One exampleof a material for this region is AlGaN),2728—a multiple quantum well used for a Blue LED (One example ofmaterials for this region are InGaN/GaN),2727—a N-type confinement layer that is used for a Blue LED (One exampleof a material for this region is GaN),2748—an oxide layer, may be preferably a conductive metal oxide such asITO,2722—an oxide layer, may be preferably a conductive metal oxide such asITO,2721—an optional reflector (e.g., a Distributed Bragg Reflector),2720—a P-type confinement layer that is used for a Green LED (Oneexample of a material for this region is GaN),2718—a buffer layer that is typically used for a Green LED (One exampleof a material for this region is AlGaN),2716—a multiple quantum well used for a Green LED (One example ofmaterials for this region are InGaN/GaN),2715—a N-type confinement layer that is used for a Green LED (Oneexample of a material for this region is GaN),2752—an oxide layer, may be preferably a conductive metal oxide such asITO,2710—an oxide layer, may be preferably a conductive metal oxide such asITO,2709—an optional reflector (e.g., a Distributed Bragg Reflector),2708—a P-type confinement layer used for a Red LED (One example of amaterial for this region is AlInGaP),2706—a multiple quantum well used for a Red LED (One example ofmaterials for this region are AlInGaP/GaInP),2704—a P-type confinement layer used for a Red LED (One example of amaterial for this region is AlInGaP),2756—an oxide layer, may be preferably a transparent conductive metaloxide such as ITO,2758—a reflector (e.g., aluminum or silver).Step (B) is illustrated in FIG. 27B. Via holes 2762 are etched to thesubstrate layer 2746 to isolate different pixels in themicrodisplay/display. Also, via holes 2760 are etched to make contactsto various layers of the stack. These via holes may be preferably filledwith a compatible oxide and the surface can be planarized with CMP.Various elements of FIG. 27B such as 2746, 2744, 2734, 2733, 2732, 2730,2728, 2727, 2748, 2722, 2721, 2720, 2718, 2716, 2715, 2752, 2710, 2709,2708, 2706, 2704, 2756 and 2758 have been described previously.Step (C) is illustrated in FIG. 27C. Metal 2764 (for example) isconstructed within the via holes 2760 using procedures similar to thosedescribed in respect to FIGS. 4A-S. Following this construction, anoxide layer 2766 is deposited. Various elements of FIG. 27C such as2746, 2744, 2734, 2733, 2732, 2730, 2728, 2727, 2748, 2722, 2721, 2720,2718, 2716, 2715, 2752, 2710, 2709, 2708, 2706, 2704, 2756, 2760, 2762and 2758 have been described previously.Step (D) is illustrated in FIG. 27D. Using procedures described inpending U.S. patent application Ser. No. 12/901,890 by authors of thispatent application, a single crystal silicon transistor layer 2768 canbe monolithically integrated using ion-cut technology atop the structureshown in FIG. 27C. This transistor layer 2768 is connected to variouscontacts of the stacked LED layers (not shown in the figure forsimplicity). Following this connection, nickel layer 2770 is constructedand solder layer 2772 is constructed. The packaging process then isconducted where the structure shown in FIG. 27D is connected to asilicon sub-mount.It can be seen that the structure shown in FIG. 27D can have each pixelemit a certain color of light by tuning the voltage given to the red,green and blue layers within each pixel. This microdisplay isconstructed using the ion-cut technology, a smart layer transfertechnique. This process where transistors are integrated monolithicallyatop the stacked RGB display can be applied to the LED conceptsdisclosed in association with FIGS. 4-10.

The embodiments of this invention described in FIGS. 26-27 may enablenovel implementations of “smart-lighting concepts” (also known asvisible light communications) that are described in “Switching LEDs onand off to enlighten wireless communications”, EETimes, June 2010 by R.Colin Johnson. For these prior art smart lighting concepts, LED lightscould be turned on and off faster than the eye can react, so signalingor communication of information with these LED lights is possible. Anembodiment of this invention involves designing thedisplays/microdisplays described in FIGS. 26-27 to transmit information,by modulating wavelength of each pixel and frequency of switching eachpixel on or off. One could thus transmit a high bandwidth through thevisible light communication link compared to a LED, since each pixelcould emit its own information stream, compared to just one informationstream for a standard LED. The stacked RGB LED embodiment described inFIGS. 4A-S could also provide a improved smart-light than prior artsince it allows wavelength tunability besides the ability to turn theLED on and off faster than the eye can react.

NuSolar Technology:

Multijunction solar cells are constructed of multiple p-n junctionsstacked atop each other. Multi-junction solar cells are oftenconstructed today as shown in FIG. 18A. A Germanium substrate 2800 istaken and multiple layers are grown epitaxially atop it. The firstepitaxial layer is a p-type doped Ge back-surface field (BSF) layer,indicated as 2802. Above it, a n-type doped Ge base layer 2804 isepitaxially grown. A InGaP hetero layer 2806 is grown above this.Following this growth, a n-type InGaAs buffer layer 2808 is grown. Atunnel junction 2810 is grown atop it. The layers 2802, 2804, 2806, and2808 form the bottom Ge cell 2838 of the multi-junction solar celldescribed in FIG. 18A. Above this bottom cell and the tunnel junction2810, a middle cell constructed of InGaAs is epitaxially grown, and isindicated as 2836. The InGaAs middle cell has the following 4 layers: ap+ doped back surface field (BSF) layer 2812 of InGaP, a p doped baselayer 2814 of InGaAs, a n doped emitter layer 2816 of InGaAs, and a n+doped window layer 2818 of InGaP. Above this InGaAs middle cell 2836, atunnel junction 2820 is grown epitaxially and above this, another cell,constructed of InGaP, and called a top cell 2834 is epitaxially grown.This top cell 2834 has the following layers: a p+ doped back-surfacefield (BSF) layer of AlInGaP 2822, a p doped base layer of InGaP 2824, an doped emitter layer of InGaP 2826 and a n+ doped window layer of AlInP2828. Above this layer of AlInP 2828, a GaAs layer 2830 is epitaxiallygrown, Aluminum contacts 2840 are deposited and an anti-reflection (AR)coating 2832 is formed. The purpose of back-surface field (BSF) layersin the multi-junction solar cell depicted in FIG. 18A is to reducescattering of carriers towards the tunnel junctions. The purpose of thewindow layers is to reduce surface recombination velocity. Both the BSFlayers and window layers are heterojunctions that help achieve the abovementioned purposes. Tunnel junctions help achieve good ohmic contactbetween various junctions in the multi-junction cell. It can be observedthat the bottom, middle and top cells in the multi-junction cell arearranged in the order of increasing band-gap and help capture differentwavelengths of the sun's spectrum.

FIG. 28B shows the power spectrum of the sun vs. photon energy. It canbe seen that the sun's radiation has energies in between 0.6 eV and 3.5eV. Unfortunately though, the multi-junction solar cell shown in FIG.28A has band-gaps not covering the solar spectrum (band-gap of cellsvaries from 0.65 eV to 1.86 eV).

FIG. 28C shows the solar spectrum and indicates the fraction of solarpower converted to electricity by the multi-junction solar cell fromFIG. 28A. It can be observed from FIG. 28C that a good portion of thesolar spectrum is not converted to electricity. This is largely becausethe band-gap of various cells of the multi-junction solar cell does notcover the entire solar spectrum.

FIGS. 29A-H show a process flow for constructing multijunction solarcells using a layer transfer flow. Although FIGS. 29A-H show a processflow for stacking two cells with two different bandgaps, it is fairlygeneral, and can be extended to processes involving more than two cellsas well. This process could include several steps that occur in asequence from Step (A) to Step (H). Many of these steps share commoncharacteristics, features, modes of operation, etc. When identicalreference numbers are used in different drawing figures, they are usedto indicate analogous, similar or identical structures to enhance theunderstanding of the present invention by clarifying the relationshipsbetween the structures and embodiments presented in the variousdiagrams—particularly in relating analogous, similar or identicalfunctionality to different physical structures.

Step (A) is illustrated in FIG. 29A. Three wafers 2920, 2940 and 2946have different materials grown or deposited above them. Materials fromthese three wafers 2920, 2940 and 2946 are stacked using layer transferto construct the multi-junction solar cell described in this embodimentof the invention. The wafer 2946 includes a substrate C denoted as 2942above which an oxide layer C, denoted as 2944, is deposited. Examples ofmaterials for 2942 include heavily doped silicon and the oxide layer C2944 could preferably be a conductive metal oxide such as ITO. The wafer2940 includes a substrate for material system B, also called substrate B2938 (e.g., InP or GaAs), a buffer layer 2936, a p++ contact layer B(e.g., InGaP) 2934, a p+ back-surface field (BSF) layer B (e.g., InGaP)2932, a p base layer B (eg. InGaAs) 2930, a n emitter layer B (e.g.,InGaAs) 2928, a n+ window layer B (e.g., InGaP) 2926, a n++ contactlayer B (e.g., InGaP) 2924 and an oxide layer B (e.g., ITO) 2922. Thewafer 2920 includes a substrate for material system A, also calledsubstrate A 2918 (e.g., InP or GaAs), a buffer layer 2916, a p++ contactlayer A (eg. AlInGaP) 2914, a p+ back-surface field (BSF) layer A (e.g.,AlInGaP) 2912, a p-base layer A (e.g., InGaP) 2910, a n-emitter layer A(e.g., InGaP) 2918, a n+ window layer A (e.g., AlInP) 2916, a n++contact layer A (e.g., AlInP) 2914 and an oxide layer A (e.g., ITO)2912. Various other materials and material systems can be used insteadof the examples of materials listed above.Step (B) is illustrated in FIG. 29B. Hydrogen is implanted into thestructure 2920 of FIG. 29A at a certain depth indicated by 2948. Variousother elements of FIG. 29B such as 2902, 2904, 2906, 2908, 2910, 2912,2914, 2916, and 2918 have been described previously. Alternatively,Helium can be implanted instead of hydrogen. Various other atomicspecies can be implanted.Step (C) is illustrated in FIG. 29C. The structure shown in FIG. 29B isflipped and bonded atop the structure indicated as 2946 in FIG. 29A.Various elements in FIG. 29C such as 2902, 2904, 2906, 2908, 2910, 2912,2914, 2916, 2944, 2942, and 2918 have been described previously.Step (D) is illustrated in FIG. 29D. The structure shown in FIG. 29C maybe cleaved at its hydrogen plane 2948 preferably using a sidewaysmechanical force. Alternatively, an anneal could be used. A CMP is thendone to planarize the surface to produce p++ contact layer A 2915.Various other elements in FIG. 29D such as 2942, 2944, 2902, 2904, 2906,2908, 2910, and 2912 have been described previously. The substrate 2918from FIG. 29C removed by cleaving may be reused.Step (E) is illustrated in FIG. 29E. An oxide layer 2950 is depositedatop the structure shown in FIG. 29D. This oxide layer 2950 may bepreferably a conductive metal oxide such as ITO, although an insulatingoxide could also be used. Various elements in FIG. 29E such as 2942,2944, 2902, 2904, 2906, 2908, 2910, 2915, and 2912 have been describedpreviously.Step (F) is illustrated using FIG. 29F. The structure indicated as 2940in FIG. 29A is implanted with hydrogen at a certain depth 2952.Alternatively, Helium or some other atomic species can be used. Variouselements of FIG. 29F such as 2922, 2924, 2926, 2928, 2930, 2932, 2934,2936, and 2938 have been indicated previously.Step (G) is illustrated in FIG. 29G. The structure shown in FIG. 29F isflipped and bonded onto the structure shown in FIG. 29E usingoxide-to-oxide bonding. Various elements in FIG. 29G such as as 2942,2944, 2902, 2904, 2906, 2908, 2910, 2912, 2915, 2950, 2922, 2924, 2926,2928, 2930, 2932, 2934, 2936, 2952, and 2938 have been indicatedpreviously.Step (H) is illustrated in FIG. 29H. The structure shown in FIG. 29G iscleaved at its hydrogen plane 2952. A CMP is then done to planarize thesurface and produces the p++ contact layer B indicated as 2935 in FIG.29H. Above this, an oxide layer 2952 (e.g., ITO) is deposited. Thesubstrate B indicated as 2938 in FIG. 29G can be reused after cleave.Various other elements in FIG. 29H such as 2942, 2944, 2902, 2904, 2906,2908, 2910, 2912, 2915, 2950, 2922, 2924, 2926, 2928, 2930, and 2932have been indicated previously.After completing steps (A) to (H), contacts and packaging are then done.One could make contacts to the top and bottom of the stack shown in FIG.29H using one front contact to ITO layer 2954 and one back contact tothe heavily doped Si substrate 2942. Alternatively, contacts could bemade to each cell of the stack shown in FIG. 29H as described in respectto FIG. 4A-S. While FIGS. 29A-H show two cells in series for themultijunction solar cell, the steps shown in the above description canbe repeated for stacking more cells that could be constructed of variousband gaps. The advantage of the process shown in FIG. 29A-H is that allprocesses for stacking are done at temperatures less than 400° C., andcould even be done at less than 250° C. Therefore, thermal expansionco-efficient mismatch may be substantially mitigated. Likewise, latticemismatch may be substantially mitigated as well. Therefore, variousmaterials such as GaN, Ge, InGaP and others which have widely differentthermal expansion co-efficients and lattice constant can be stacked atopeach other. This flexibility in use of different materials may enable afull spectrum solar cell or a solar cell that covers a increased bandwithin the solar spectrum than the prior art cell shown in FIG. 28A.

FIGS. 30A-D show a process flow for constructing another embodiment ofthis invention, a multi-junction solar cell using a smart layer transfertechnique (ion-cut). This process may include several steps that occurin a sequence from Step (A) to Step (D). Many of these steps sharecommon characteristics, features, modes of operation, etc. Whenidentical reference numbers are used in different drawing figures, theyare used to indicate analogous, similar or identical structures toenhance the understanding of the present invention by clarifying therelationships between the structures and embodiments presented in thevarious diagrams—particularly in relating analogous, similar oridentical functionality to different physical structures.

Step (A) is illustrated in FIG. 30A. It shows a multi-junction solarcell constructed using epitaxial growth on a heavily doped Ge substrate,as described in the prior art multi-junction solar cell of FIG. 28A. Thestructure shown in FIG. 30A includes the following components:3002—a Ge substrate,3004—a p-type Ge BSF layer,3006—a n-type Ge base layer,3008—a InGaP hetero layer,3010—a n-type InGaAs buffer layer,3012—a tunnel junction,3014—a p+ InGaP BSF layer,3016—a p-type InGaAs base layer,3018—a n-type InGaAs emitter layer,3020—a n+ InGaP window layer,3022—a tunnel junction,3024—a p+ AlInGaP BSF layer,3026—a p-type InGaP BSF layer,3028—a n-type InGaP emitter layer,3030—a n+− type AlInP window layer, and3032—an oxide layer, may be preferably of a conductive metal oxide suchas ITO.Further details of each of these layers is provided in the descriptionof FIG. 28A.Step (B) is illustrated in FIG. 30B. Above a sapphire or SiC or bulk GaNsubstrate 3034, various layers such as buffer layer 3036, a n+ GaN layer3038, a n InGaN layer 3040, a p-type InGaN layer 3042 and a p+ GaN layer3044 are epitaxially grown. Following this growth, an oxide layer 3046may be constructed preferably of a transparent conducting oxide such as,for example, ITO is deposited. Hydrogen is implanted into this structureat a certain depth indicated as 3048. Alternatively, Helium or someother atomic species can be implanted.Step (C) is illustrated in FIG. 30C. The structure shown in FIG. 30B isflipped and bonded atop the structure shown in FIG. 30A usingoxide-to-oxide bonding. Various elements in FIG. 30C such as 3002, 3004,3006, 3008, 3010, 3012, 3014, 3016, 3018, 3020, 3022, 3024, 3026, 3028,3030, 3032, 3048, 3046, 3044, 3042, 3040, 3038, 3036, and 3034 have beendescribed previously.Step (D) is illustrated using FIG. 30D. The structure shown in FIG. 30Cis cleaved at its hydrogen plane 3048. A CMP process is then conductedto result in the n+ GaN layer 3041. Various elements in FIG. 30D such as3002, 3004, 3006, 3008, 3010, 3012, 3014, 3016, 3018, 3020, 3022, 3024,3026, 3028, 3030, 3032, 3046, 3044, 3042, and 3038 have been describedpreviously.After completing steps (A) to (D), contacts and packaging are then done.Contacts may be made to the top and bottom of the stack shown in FIG.30D, for example, one front contact to the n+ GaN layer 3041 and oneback contact to the heavily doped Ge substrate 3002. Alternatively,contacts could be made to each cell of the stack shown in FIG. 30D asdescribed in FIGS. 4A-S.

FIGS. 29-30 described solar cells with layer transfer processes.Although not shown in FIG. 29-30, it will be clear to those skilled inthe art based on the present disclosure that front and back reflectorscould be used to increase optical path length of the solar cell andharness more energy. Various other light-trapping approaches could beutilized to boost efficiency as well.

An aspect of various embodiments of this invention is the ability tocleave wafers and bond wafers at lower temperatures (e.g., less than400° C.). In pending U.S. patent application Ser. No. 12/901,890 byauthors of this invention, several techniques to reduce temperatures forcleave and bond processes are described. These techniques are hereinincorporated in this document by reference.

Several material systems have been quoted as examples for variousembodiments of this invention in this patent application. It will beclear to one skilled in the art based on the present disclosure thatvarious other material systems and configurations can also be usedwithout violating the concepts described. It will also be appreciated bypersons of ordinary skill in the art that the present invention is notlimited to what has been particularly shown and described hereinabove.Rather, the scope of the present invention includes both combinationsand sub-combinations of the various features described hereinabove aswell as modifications and variations which would occur to such skilledpersons upon reading the foregoing description. Thus the invention is tobe limited only by the appended claims.

1-13. (canceled)
 14. A method of forming a display device comprising aplurality of pixels controlled by transistors, the method comprising:activating dopants in a monocrystalline layer, subsequently usingion-cut to transfer said monocrystalline layer onto a glass or plasticsubstrate, and forming said transistors, wherein forming saidtransistors comprises at least one of: forming a recessed channeltransistor by etching an etched recess between a source region and adrain region, and forming a gate in the etched recess, forming areplacement gate transistor by forming a dummy gate and subsequentlyremoving the dummy gate, or forming a junctionless transistor.
 15. Amethod for forming a display device according to claim 14, wherein saidtransistors are processed on said glass or plastic substrate at aprocess temperature of less than 400° C.
 16. A method for forming adisplay device according to claim 14, wherein said transistors areprocessed on said glass or plastic substrate at a process temperature ofless than 600° C.
 17. A method for forming a display device according toclaim 14, wherein said display comprises at least one mono-crystallizedlayer transferred using ion-cut.
 18. A method for forming a displaydevice according to claim 14, further comprising: etching said displayto define at least one hundred individual pixels.